Methods, systems and apparatus for scheduling of subframes and hybrid automatic repeat request (HARQ) feedback

ABSTRACT

Methods, systems and apparatus are provided for hybrid automatic repeat request (HARQ) processes. A wireless transmit/receive unit (WTRU) may receive, in a first subframe, downlink control information (DCI) including a grant for a physical downlink shared control channel (PDSCH) and an indication of physical uplink control channel (PUCCH) resources. Further, the WTRU may receive, in the first subframe, data on the PDSCH based on the grant. Also, the WTRU may generate first acknowledgement (ACK)/negative ACK (NACK) information based on the data received on the PDSCH. Accordingly, the WTRU may transmit, in the first subframe, the first ACK/NACK information in a PUCCH transmission. In an example, the first ACK/NACK information may be transmitted in a time slot in the first subframe different from a time slot in the first subframe in which the DCI is received. Also, transmitting the PUCCH transmission may have a duration of one or two symbols.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/072,557, which is the U.S. National Stage, under 35 U.S.C. § 371, ofInternational Application No. PCT/US2017/016438 filed Feb. 3, 2017,which claims the benefit of U.S. Provisional Application Ser. No.62/290,770 filed Feb. 3, 2016 and U.S. Provisional Application Ser. No.62/334,759 filed May 11, 2016, the contents of which are herebyincorporated by reference herein.

BACKGROUND

With new applications emerging for cellular technology, such as alarmreporting, automotive safety, and factory process control, theimportance of low latency cellular communications, including machinetype communications (MTC), has rapidly increased. For example, in along-term evolution (LTE) Advanced (LTE-A) system, the typical 1 mstransmission time interval (TTI) and associated latencies may no longerbe sufficient. Existing applications such as gaming and real-timeapplications like Voice Over LTE (VoLTE) and videotelephony/conferencing, may also benefit from reduced latency in termsof, for example, increased perceived quality of experience.

One or more components may contribute to the total end-to-end delay forconnected wireless transmit/receive units (WTRUs). These components mayinclude, for example, one or more of scheduling grant acquisition time,TTI, processing time, and hybrid automatic repeat request (hybrid ARQ orHARQ) round-trip time (RTT). Shortening one or more of these componentsmay reduce the total end-to-end latency.

SUMMARY

Methods, systems and apparatus are provided for uplink (UL) and downlink(DL) transmission including hybrid automatic repeat request (HARQ)transmission corresponding to different transmission time interval (TTI)lengths. For example, the transmission may be based on configuring abuffer to be shared by a plurality of HARQ processes corresponding to atleast a normal transmission time interval (nTTI) having an nTTI lengthand a short TTI (sTTI) having an sTTI length that is shorter than thenTTI length.

In an example, a wireless transmit/receive unit (WTRU) may link a firstHARQ process and a second HARQ process, wherein the first HARQ processis associated with a first HARQ buffer and a first TTI length and thesecond HARQ process is associated with the first HARQ buffer and asecond TTI length. The WTRU may transmit a first transport block (TB)using the linked first HARQ process and the first HARQ buffer. Further,the WTRU may receive a UL grant. Also, the WTRU may determine that thereceived UL grant is for a new transmission for the linked second HARQprocess. The WTRU may then release the first HARQ buffer based on adetermination that the received UL grant is for the new transmission forthe linked second HARQ process. In addition, the WTRU may generate asecond TB for the new transmission and store the new TB in the firstHARQ buffer. Further, the WTRU may transmit the second TB using thelinked second HARQ process and the first HARQ buffer.

In an example, the first TB and the second TB may be medium accesscontrol (MAC) protocol data units (PDUs). Further, the first TB maycontain data associated with a first TTI and the second TB may containdata associated with a second TTI.

In an additional example, a WTRU may link a first HARQ process and asecond HARQ process, wherein the first HARQ process is associated with afirst HARQ buffer and a first TTI length and the second HARQ process isassociated with the first HARQ buffer and a second TTI length. Further,the WTRU may receive data for a first TB using the linked first HARQprocess and the first HARQ buffer. The WTRU may also receive a DL grant.The WTRU may then determine that the received DL grant is for thereception of a new transmission for the linked second HARQ process.Further, the WTRU may release the first HARQ buffer based on adetermination that the received DL grant is for the reception of the newtransmission for the linked second HARQ process. Also, the WTRU mayreceive data for a second TB for the new transmission using the linkedsecond HARQ process and the first HARQ buffer. Further, the WTRU mayreplace the data in the first HARQ buffer with the data received for thesecond TB.

In another example, the HARQ buffers may be used for soft combining. Forexample, the first HARQ buffer may be used for soft combining. In anadditional example, the HARQ buffers may be located in soft buffermemory. For example, the first HARQ buffer may be located in soft buffermemory.

In an additional example, a WTRU may receive a time division duplex(TDD) UL/DL subframe configuration. Further, the WTRU may receive a DLgrant with an indication to use a special subframe for a physical uplinkcontrol channel (PUCCH) transmission. The WTRU may then dynamicallydetermine which subframe to switch to a special subframe. The WTRU mayswitch the subframe to a special subframe. Further, the WTRU maydetermine a special subframe configuration to use for the determinedspecial subframe. Also, the WTRU may determine resources of thedetermined special subframe to use for a PUCCH.

The WTRU may then determine PUCCH resources and PUCCH design parametersfor the PUCCH. Further, the WTRU may transmit HARQ feedback on the PUCCHin a UL portion in the determined resources of the determined specialsubframe with the determined special subframe configuration using thedetermined PUCCH resources and PUCCH design parameters.

In a further example, a WTRU may receive, in a first subframe, downlinkcontrol information (DCI) including a grant for a physical downlinkshared control channel (PDSCH) and an indication of PUCCH resources.Further, the WTRU may receive, in the first subframe, data on the PDSCHbased on the grant. Also, the WTRU may generate first acknowledgement(ACK)/negative ACK (NACK) information based on the data received on thePDSCH. Accordingly, the WTRU may transmit, in the first subframe, thefirst ACK/NACK information in a PUCCH transmission.

In an example, the first ACK/NACK information may be transmitted in atime slot in the first subframe different from a time slot in the firstsubframe in which the DCI is received. Also, transmitting the PUCCHtransmission may have a duration of one or two symbols. Further, thefirst subframe may have a downlink portion and an uplink portion.Moreover, the data received on the PDSCH may be received in the downlinkportion and the first ACK/NACK information may be transmitted in theuplink portion.

In a further example, a number of symbols for receiving data on a PDSCHmay vary for the WTRU. Also, the DCI may include a HARQ processidentifier associated with the data received on the PDSCH. Further, thedata may be received over a number of symbols different from a number ofsymbols for a reception of a retransmission of the data. In addition,second ACK/NACK information may be transmitted on the PUCCH in at leastone of the first subframe and a second subframe.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a table illustrating an example of time division duplex (TDD)uplink (UL)/downlink (DL) configurations;

FIG. 3 is a table illustrating an example of special subframeconfigurations;

FIG. 4 is a table illustrating an example of special subframeconfigurations in terms of symbols;

FIG. 5A is a table illustrating an example of UL-DL configurations forslot-based transmission time intervals (TTIs);

FIG. 5B is a diagram illustrating an example of sending hybrid automaticrepeat request (HARQ) feedback on a switched special subframe in aconfiguration supporting a short TTI (sTTI);

FIG. 6 is a diagram illustrating an example of HARQ feedback latencywith and without short physical uplink control channel (sPUCCH)transmission in uplink pilot timeslots (UpPTSs) of special subframes;

FIG. 7A is a diagram illustrating an example of transmitting HARQfeedback on a physical uplink control channel (PUCCH) in a UL portion indetermined resources of a determined special subframe with a determinedspecial subframe configuration;

FIG. 7B is a diagram illustrating an example of a guard-band physicalresource block (PRB) configuration for HARQ feedback;

FIG. 8 is a diagram illustrating an example of a TDD configuration forguard-band PRBs (G-PRBs) based on a TDD configuration for systembandwidth PRBs (S-PRBs);

FIG. 9 is a diagram illustrating an example of timing offset betweenS-PRBs and G-PRBs;

FIG. 10 is a diagram illustrating an example of a HARQ feedback resourcedetermination;

FIG. 11 is a diagram illustrating an example of separate HARQ processesand HARQ buffers for two TTI lengths;

FIG. 12 is a diagram illustrating another example of separate HARQprocesses and HARQ buffers for two TTI lengths;

FIG. 13 is a diagram illustrating an example of linking or sharing HARQprocesses, HARQ buffers or both between two TTI lengths;

FIG. 14 is a diagram illustrating an example timeline for multiple TTIlength usage;

FIG. 15 is a diagram illustrating another example of HARQ processes,buffers or both that may be linked, shared or overlapped;

FIG. 16 is a diagram illustrating another example of linking, sharing oroverlapping HARQ processes, buffers or both;

FIG. 17 is a diagram illustrating a further example of linking, sharingor overlapping HARQ processes, buffers or both;

FIG. 18 is a diagram illustrating an example of linking or sharing HARQprocesses, buffers or both with a dynamic indication; and

FIG. 19 is a diagram illustrating an example of HARQ buffer sharing bydifferent HARQ processes.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (for example, radio frequency(RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.).The air interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (for example, WCDMA, CDMA2000, GSM,LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG.1A, the base station 114 b may have a direct connection to the Internet110. Thus, the base station 114 b may not be required to access theInternet 110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (for example, the basestation 114 a) over the air interface 116. For example, in oneembodiment, the transmit/receive element 122 may be an antennaconfigured to transmit and/or receive RF signals. In another embodiment,the transmit/receive element 122 may be an emitter/detector configuredto transmit and/or receive IR, UV, or visible light signals, forexample. In yet another embodiment, the transmit/receive element 122 maybe configured to transmit and receive both RF and light signals. It willbe appreciated that the transmit/receive element 122 may be configuredto transmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (for example, multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (for example, a liquid crystal display (LCD)display unit or organic light-emitting diode (OLED) display unit). Theprocessor 118 may also output user data to the speaker/microphone 124,the keypad 126, and/or the display/touchpad 128. In addition, theprocessor 118 may access information from, and store data in, any typeof suitable memory, such as the non-removable memory 130 and/or theremovable memory 132. The non-removable memory 130 may includerandom-access memory (RAM), read-only memory (ROM), a hard disk, or anyother type of memory storage device. The removable memory 132 mayinclude a subscriber identity module (SIM) card, a memory stick, asecure digital (SD) memory card, and the like. In other embodiments, theprocessor 118 may access information from, and store data in, memorythat is not physically located on the WTRU 102, such as on a server or ahome computer (not shown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (for example, nickel-cadmium(NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion(Li-ion), etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (for example, longitudeand latitude) regarding the current location of the WTRU 102. Inaddition to, or in lieu of, the information from the GPS chipset 136,the WTRU 102 may receive location information over the air interface 116from a base station (for example, base stations 114 a, 114 b) and/ordetermine its location based on the timing of the signals being receivedfrom two or more nearby base stations. It will be appreciated that theWTRU 102 may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity gateway (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (forexample, an IP multimedia subsystem (IMS) server) that serves as aninterface between the core network 106 and the PSTN 108. In addition,the core network 106 may provide the WTRUs 102 a, 102 b, 102 c withaccess to the networks 112, which may include other wired or wirelessnetworks that are owned and/or operated by other service providers.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

One or more time components may contribute to the total end to end delayfor connected WTRUs. These components may include, for example, one ormore of scheduling grant acquisition time, transmission time interval(TTI), processing time, and hybrid-ARQ (HARQ) round-trip time (RTT).

The transmission of a request, grant, HARQ feedback, and/or data may bedone in and/or according to the timing of blocks or chunks, for example,subframes, which may have a fixed or known duration (for example, 1 ms).The fixed duration may be referred to as a TTI.

Processing time may be or may include time needed or used to process(for example, encode and/or decode) data and/or control signaling orinformation, for example, at or by a WTRU and/or an eNode-B. Dataprocessing time may be proportional to the transport block (TB) size ofthe data.

HARQ RTT may be a function of one or more of: the time relationshipbetween a scheduling grant and the associated transmission (for example,the scheduled transmission) by the sender, the time relationship betweena transmission by a sender and when HARQ feedback (for example,acknowledgement (ACK), negative acknowledgement (NACK), orretransmission request) from the receiver may be transmitted, and thetime relationship between when HARQ feedback may be transmitted by thereceiver and a retransmission by the sender. For example, for an uplink(UL) transmission in frequency division duplex (FDD), the HARQacknowledgement for a packet received by the eNode-B in subframe n maybe reported in subframe n+4. A retransmission, for example, if needed bythe WTRU, may be sent in subframe n+8. This may correspond to a HARQ RTTof 8 ms. For a system employing time division duplex (TDD), HARQ RTT maydepend on the TDD configuration (for example, the UL/downlink (DL)configuration) and may be at least 8 ms. For an LTE DL transmission, theHARQ scheme may be asynchronous. The HARQ feedback may be available atsubframe n+k where k may be 4 for FDD and at least 4 for TDD, forexample, depending on the TDD configuration. Retransmissions may bescheduled in subframe n+k+k1 or later. In this case, k1 may be 4 for FDDand at least 4 for TDD, for example, depending on the TDD configuration.

FIG. 2 is a table illustrating an example of TDD UL/DL configurations.For TDD, multiple TDD UL/DL subframe configurations 210 may be supportedand at least one of the configurations may be used in an eNode-B. EachTDD UL/DL subframe configuration may contain one or more downlinksubframes ‘D’, uplink subframes ‘U’, and special subframes ‘S’. ExampleTDD UL/DL subframe configurations 210, including the types of subframeslisted by subframe number 230 and the downlink-to-uplink switch-pointperiodicity 220, are shown in table 200. Special subframes may include aDL part, a UL part and a guard period between DL and UL parts, forexample, to allow time for the transition from DL to UL. A specialsubframe may be referred to as a mixed subframe and the terms may beused interchangeably herein.

A subframe, as depicted in FIG. 2, may have a duration of 1 ms. However,it will be appreciated that a subframe is not limited to such aduration, and may be implemented with any length of time as a matter ofdesign choice. Uplink-downlink subframe configuration anduplink-downlink configuration may be used interchangeably herein. Asubframe is used herein as a non-limiting example of a time unit. Anyother time unit may be substituted for subframe and still be consistentwith this disclosure. Some example time units include symbol, slot,timeslot, and the like.

FIG. 3 is a table illustrating an example of special subframeconfigurations. As shown in table 300, each of the special subframeconfigurations 310 may use a normal cyclic prefix in the downlink 320 oran extended cyclic prefix in the downlink 360. The downlink part of thespecial subframe may be referred to as the downlink pilot timeslot(DwPTS) and the uplink part of the special subframe may be referred toas the uplink pilot timeslot (UpPTS). The special subframe may alsoinclude a guard period (GP).

The lengths of the parts of the special subframe may be given as afunction of a sampling time (Ts). The sampling time may be (10ms)/307,200, for example. However, it will be appreciated that asampling time is not limited thereto and other lengths of time may beused for a T_(S). In an example as shown in table 300, the specialsubframe configurations 310 may use a DwPTS 330 and a UpPTS 340 when anormal cyclic prefix is used in the downlink 320 and may use a DwPTS 370and a UpPTS 380 when an extended cyclic prefix is used in the downlink360. Further, the special subframe configurations 310 may be used with anormal cyclic prefix in the uplink 345 or an extended cyclic prefix inthe uplink 350 when using a normal cyclic prefix in the downlink 320,and a normal cyclic prefix in the uplink 385 or an extended cyclicprefix in the uplink 390 when using an extended cyclic prefix in thedownlink 360. Examples lengths of the parts of the respective parts ofthe special subframe are shown in table 300. Further, in the exampleshown in table 300, special subframe configurations 8 and 9 may not beused with an extended cyclic prefix in the downlink 360, however inother examples special subframe configurations 8 and 9 may be used withan extended cyclic prefix in the downlink.

FIG. 4 is a table illustrating an example of special subframeconfigurations in terms of symbols. For example, 14 symbols per 1 mssubframe may be used. The symbols may, for example, be orthogonalfrequency division multiplexing (OFDM) or SC-FDMA symbols. As shown intable 400, for each special subframe configuration 410 the length of theparts of the special subframe may be expressed in samples 420 or insymbols 460. The special subframe configurations may be used with anormal cyclic prefix (CP). For example, for each special subframeconfiguration 410 the special subframe's DwPTS 430, GP 450 and UpPTS 440may be expressed in samples 420, as shown in table 400. Also, as shownin table 400, for each special subframe configuration 410 the length ofthe special subframe's DwPTS 470, GP 490 and UpPTS 480 may be in symbols460. The length in symbols may be an approximation.

Various TDD configurations are provided herein. In a TDD system, theremay be one or more UL-DL configurations used in a cell. Theconfigurations may include a configuration (ConfigCell) that may becell-specific. ConfigCell may be used by some WTRUs for one or more (or,for example, all) of subframe directions, scheduling timing and/or HARQtiming. For some WTRUs, ConfigCell may be used for UL scheduling timingand/or UL HARQ timing. UL scheduling timing may be or may include therelationship between UL grant reception and UL transmission. Forexample, UL scheduling timing may be or may include the identificationof which DL subframe may be used to schedule transmission in which ULsubframe. UL HARQ timing may be or may include at least one of therelationship between UL transmission and HARQ feedback transmission (forexample, on a physical HARQ indicator channel (PHICH)) in the DL, and/orthe relationship between HARQ feedback in the DL and a retransmission inthe UL. As used herein, the term relationship may mean timingrelationship. ConfigCell may be indicated by a cell in broadcastsignaling (for example, in a system information block (SIB) such asSIB1).

The configurations may include a configuration (ConfigHARQD) that may beWTRU-specific. ConfigHARQD may be used by some WTRUs for DL HARQ timing.DL HARQ timing may be or may include the relationship between receptionin the DL and a HARQ feedback transmission in the UL (for example, on aphysical uplink control channel (PUCCH)). ConfigHARQD may be configuredin a WTRU via dedicated signaling.

The subframe directions in ConfigCell and ConfigHARQD may not be thesame. For example, some of the UL subframes in ConfigCell may beindicated as DL or special subframes in ConfigHARQD. The subframes thatare not the same direction in ConfigCell and ConfigHARQD may be referredto as flexible subframes. The configurations may include anotherconfiguration (for example, ConfigDir) that may be used to indicate thesubframe directions to use, for example, for the flexible subframes.ConfigDir may be provided in signaling that may be dynamic, for example,in a downlink control information (DCI) format. ConfigDir may beprovided to the WTRU periodically.

The three configurations (i.e., ConfigCell, ConfigHARQD and ConfigDir)may be used together to dynamically change the direction of somesubframes (for example, from UL to DL) for at least some WTRUs. Theconfigurations may be provided or transmitted by an eNode-B. Theconfigurations may be received and/or used by a WTRU.

Reserved subframes may be provided and/or used. Subframes may beconfigured in a WTRU that may be intended for at least a particular use.Such subframes may be referred to as reserved subframes. For example,subframes in an LTE system may be configured and/or reserved for use forMultimedia Broadcast Multicast Services (MBMS). These subframes may bereferred to as multicast-broadcast single-frequency network (MBSFN)subframes. Subframes such as subframes 3, 4, 7, 8 and/or 9 shown in FIG.2, may be configured and/or identified as MBSFN subframes.

DL reserved subframes or MBSFN subframes may include a DL control regionand a data region. The DL control region may include a channel that mayindicate the number of symbols in the DL control region (for example, aphysical control format indicator channel (PCFICH)). The DL controlregion may include one or more DL control channels (for example, aphysical downlink control channel (PDCCH)) that may provide grants forDL data or UL data. The DL control region may include one or more DLcontrol channels (for example, a PDCCH) that may provide a trigger orrequest for transmission of a sounding reference signal (SRS) or channelstate information (CSI) feedback. The DL control region may include oneor more HARQ feedback channels (for example, a PHICH) that may be usedin the DL to indicate ACK and/or NACK for UL data reception. The controlregion may include cell-specific reference signals (CRS). The dataregion may not include CRS, for example, when there may be no datatransmission in the data region.

Reserved subframes, such as MBSFN subframes, may be used for otherpurposes. MBSFN subframes may be used in the examples herein as anon-limiting example of reserved subframes.

Some WTRUs may perform blind decoding in a reserved subframe. Forexample. A WTRU may monitor for a DL control channel (for example aPDCCH) in the DL control region of a reserved subframe. A WTRU maymonitor for a DL control channel (for example an enhanced PDCCH(EPDCCH)) in the data region of a reserved subframe. The WTRU may act inaccordance with the DL control channel (for example, a PDCCH or EPDCCH),for example, when the WTRU successfully decodes the channel.

A node (for example, an eNode-B) or a device (for example, a WTRU) mayhave at least one medium access control (MAC) entity. A WTRU or MACentity may have at least one HARQ entity. For example, there may be a(for example, one) HARQ entity at the MAC entity for a serving cell (forexample, for each serving cell). For UL (for example, for a ULdirection), there may be a (for example, one) HARQ entity at the MACentity for a (for example, each) serving cell with configured UL. Aserving cell may be a cell with which a WTRU may communicate and/or acell with which a WTRU may be connected.

A WTRU, MAC entity or HARQ entity may maintain a number of parallel HARQprocesses. A WTRU, MAC entity or HARQ entity may maintain a number ofparallel HARQ processes for at least one transmission type or directionsuch as UL, DL, or sidelink (SL). In one or more embodiments, eight (8)may be used as a non-limiting number of HARQ processes for atransmission direction. It is understood that any other number may beused, including zero (0), for a transmission direction and the number ofHARQ processes may be different for different transmission directions.

A use of parallel HARQ processes may enable transmissions to take placecontinuously while waiting for HARQ feedback on successful orunsuccessful reception of previous transmissions.

A WTRU, MAC entity, and HARQ entity may be used interchangeably herein.In one or more embodiments and examples described herein, a MAC entityand a HARQ entity may be used as non-limiting examples of an entity thatmay maintain, include, comprise, or manage HARQ processes and/or HARQprocessing. Transmission type and transmission direction may also beused interchangeably. In one or more embodiments and examples describedherein, UL, DL, and SL may be used as non-limiting examples of atransmission direction or type. UL, DL, and SL may further refer to aUL, DL, or SL channel established or used for UL, DL, or SLtransmissions. UL, DL, and SL may be substituted for each other in oneor more embodiments and examples described herein and still beconsistent with the examples provided herein.

Furthermore, a HARQ process may be associated with a HARQ processidentity or identifier that may, for example, be referred to as a HARQprocess ID. A HARQ process may be associated with a HARQ buffer. Abuffer (for example, a HARQ buffer) may be or may comprise a softbuffer.

A soft buffer may be used for soft combining coded bits from one or morerepetitions or retransmissions of a TB of data. For example, in wirelesscommunication systems such as 3rd Generation Partnership Project (3GPP)LTE cellular communication systems, data associated with one or morereceived messages may be stored in so-called soft buffer memory that maybe used to store so-called soft information associated with receivedbits, which may also be referred to as soft bits. The soft informationfor a received bit may contain the most likely value of the bit and/or ameasure of its reliability (for example, an estimate of the receivedsignal energy relative to a noise level). The term “soft information” or“soft bit” generally refers to not making a hard decision about thevalue of a bit during demodulation and/or input to a decoder, which mayalso be referred to as a soft decision. These measures of reliabilitymay be used to enhance decoding performance. For example, a decodedreceived packet and its supporting data (for example, soft bits) may begenerally stored in soft buffer memory, for example to accommodatecombining the data with retransmitted data in the event that adetermination is made that the packet was received in error for aprevious transmission or previous retransmission. A HARQ signal mayrequest that the data be retransmitted so that, for example,retransmitted data may be combined in the receiver with the originallyreceived packet.

A retransmission of a TB may include the same or different coded bits asthe original (for example, new) transmission or another retransmissionof the TB. A buffer may be or may represent memory, for example, anamount of memory that may be in a denomination such as bits or bytes.The memory of a buffer may comprise adjacent and/or non-adjacent piecesor blocks of memory.

A shorter TTI may be used, for example to reduce total end to end delayfor connected WTRUs and/or or to reduce latency. Shortening the TTIalone, however, may not be sufficient since HARQ RTT may play asignificant role in end-to-end latency. To shorten the HARQ RTT,resources for feedback and retransmission may need to be availablesooner (for example, sooner than for a regular, legacy or longer TTI).In a system in which separate carrier frequencies may be used for UL andDL, for example, an FDD system, HARQ timing may not be impacted byavailability of resources for feedback and retransmission. For example,UL resources for acknowledging DL reception may be readily available. Ina system in which the same carrier frequency may be used for both UL andDL, for example, a TDD system, the ability to shorten the HARQ timingmay be impacted by the availability of resources for feedback andretransmission. For example, for HARQ feedback desired in the UL at n(for example, 4) times the TTI after a DL data transmission, the carriermay not be available for use in the UL at n times the TTI. Carrieravailability may, for example, depend on the TTI and the uplink-downlinkconfiguration.

Scheduling and HARQ feedback timing based on using one or more newspecial subframe configurations may reduce latency in an LTE Advancedsystem. A new special subframe configuration may allow one or more ofthe following. A new configuration may allow PUCCH transmission and/orphysical uplink shared channel (PUSCH) transmission in the UL in aspecial subframe. Also, a new configuration may allow multiple DL and ULparts in a special subframe. Further, a new configuration may allow DLgrants and HARQ feedback in the same subframe. In addition, a newconfiguration may allow UL grants and UL data transmission in the samesubframe.

A special subframe may be a mixed UL/DL subframe. A special subframe maybe a subframe with at least one UL part and at least one DL part. Theterms part, portion, and region may be used interchangeably herein. Aspecial subframe may be a subframe comprising a set of parts and/or timeunits (for example, time samples, symbols, slots and the like) that maybe configured and/or used for UL and/or DL. Configuration may besemi-static or dynamic.

Special subframes may be used, for example, with short TTIs (sTTIs) orslot based transmission. Special subframes (for example, additionalspecial subframes) may be used for HARQ feedback. Special subframes (forexample, additional special subframes) may be used to reduce the latencyfor HARQ feedback.

Slot based transmission may be a way to shorten a TTI (for example, fromsubframe based transmission), however, shortening (or, for example, onlyshortening) the TTI may not be sufficient, for example, for reducinglatency in a TDD system.

FIG. 5A is a table illustrating an example of UL-DL configurations forslot-based TTIs. As shown in an example in table 500, each UL-DLconfiguration 510 may contain one or more DL or D slots and one or moreUL or U slots 515. For example, there may be seven (7) configurationsnumbered 0 through 6 and there may be twenty (20) slots, numbered 0through 19. For these subframes, there may be a guard period of a numberof time samples or symbols, such as shown in FIG. 4, such that a slotmay not be fully utilized in either DL and/or UL. In FIG. 5A, for DLtransmission in slot 9 of configuration 4, feedback may not betransmitted until the next occurrence of slot 3 or 4. Thus, latencyreduction may be limited by the UL-DL configuration.

Special subframes may be substituted for UL and/or DL subframes, forexample, to send HARQ feedback. Special subframes may comprise at leastone DL part and at least one UL part. Special subframes may comprise atleast one GP or gap. GP, gap, and gap period may be used interchangeablyherein. A gap may be of length 0 or greater than 0 length. A gap may berepresented in time units such as Ts or symbols.

The substitution of special subframes for DL and/or flexible subframesmay, for example, enable additional opportunities for UL transmission.Examples of the substitution of special subframes are provided herein. Aspecial subframe may be substituted for one or more of the following. Aspecial subframe may be substituted for a subframe that may be indicatedas a UL subframe in ConfigCell (for example, for a cell). Also, aspecial subframe may be substituted for a subframe that may be indicatedas a DL subframe in a ConfigHARQD that may be configured in or receivedby one or more WTRUs. Further, a special subframe may be substituted fora subframe that may be indicated as a DL subframe in a ConfigDir thatmay be configured in or received by one or more WTRUs. In addition, aspecial subframe may be substituted for a subframe that may beconsidered as a flexible subframe by one or more WTRUs. In anotherexample, a special subframe may be substituted for a subframe that maybe indicated or configured as an MBSFN subframe, for example, in a cell.Moreover, a special subframe may be substituted for a subframe that maybe indicated or configured as an MBSFN subframes via broadcast ordedicated signaling.

A special subframe with a first configuration may be substituted for aspecial subframe with a second configuration. The first configurationmay have a same gap as the second configuration, or the firstconfiguration may have a smaller gap or larger gap than the secondconfiguration. The second configuration may be provided incell-specific, for example, broadcast, signaling such as in a SIB. Thefirst configuration may be provided in dedicated and/or dynamicsignaling. The first configuration may have a larger UL region than thesecond configuration. The first configuration may have a larger DLregion than the second configuration. The first configuration may havemore DL and/or UL regions than the second configuration.

For example, the second special subframe configuration, the specialsubframe configuration that may be cell-specific, and/or the specialsubframe configuration that may be provided in a SIB may be a specialsubframe configuration with a large gap, for example, special subframeconfiguration 0 or 5 in FIG. 4 which shows a GP of 10 symbols and 9symbols, respectively. A configuration with a large gap may beindicated, for example, in a cell that does not need a large gap. Thegap may be used to allow for delay or timing advance. A large gap may beneeded or used in a large cell. A configuration with a large gap may beindicated or used in a small cell, for example, to enable a WTRU whichmay understand a new special subframe (for example, with a larger ULand/or DL region) to use that special subframe in place of the SIBconfigured special subframe.

Substitution may be performed according to a configuration that may bebroadcast, WTRU specific, and/or WTRU-group specific. A configurationmay be provided by an eNode-B or a cell. A configuration may be providedvia physical layer signaling such as in a DCI format. A configurationmay be provided via higher layer signaling such as radio resourcecontrol (RRC) signaling or broadcast signaling.

A special subframe may include and/or may begin with a DL part. A DLpart may include at least part of a DL control region. One or more of aPCFICH, PHICH, PDCCH, EPDCCH, and/or CRS may be included in a DL controlregion. A DL part may be followed by a UL part. There may be a gap, forexample, with no transmission between the DL part and the UL part. A DLpart may include a DL data region. Further, one or more of a EPDCCHand/or a physical downlink shared channel (PDSCH) may be included in aDL data region.

An eNode-B may transmit in a DL part. An eNode-B may transmit in a DLcontrol region. An eNode-B may transmit at least one of a PCFICH, PHICH,PDCCH, EPDCCH, and/or CRS in a DL part and/or a DL control region. AneNode-B may transmit a EPDCCH and/or PDSCH in a DL data part and/or DLdata region.

A WTRU may receive in a DL part. An WTRU may receive in a DL controlregion. A WTRU may monitor for and/or receive at least one of a PCFICH,PHICH, PDCCH, EPDCCH, and/or CRS in a DL part and/or a DL controlregion. An WTRU may monitor for and/or receive a EPDCCH and/or PDSCH ina DL data part and/or DL data region.

A UL part may be used to carry UL control information such as a PUCCH. AUL part may be used to carry UL data such as a PUSCH. The PUCCH and/orPUSCH design may be adapted based on the special subframe configuration,for example, based on a UL portion of the special subframe.

A WTRU may transmit in a UL part. A WTRU may transmit at least one of aPUCCH and/or PUSCH in a UL part. An eNode-B may receive in a UL part. AneNode-B may receive one or more of a PUCCH and/or PUSCH in a UL part.

In an example of special subframe configurations shown in FIG. 4, a ULportion may be limited to 1 or 2 symbols. To use a special subframe fora PUCCH and/or PUSCH, the UL portion may be larger. In exampleconfigurations shown in table 400, the gap sizes may be up to 10symbols. The large number of symbols may correspond to cells as large as100 km. However, such a large number of gap symbols may not be used forsmaller cells.

Other special subframe configurations may be used. For example, aspecial subframe configuration may contain at least one or more of thefollowing. In an example configuration, a special subframe may contain aUL part followed by a DL part, for example, without a gap between the ULand DL parts.

Also, in an example configuration, a special subframe may contain a gapfollowed by a UL part. The gap followed by the UL part may begin at thestart of the special subframe, for example, when the special subframemay follow a DL subframe or when the special subframe may follow asubframe where the last part of that subframe may be a DL part.

In addition, in an example configuration, a special subframe may containa DL part followed by a gap. The DL part followed by the gap may be atthe end of the special subframe, for example, when the next subframe maybe a UL subframe or when the first part of the next subframe may be a ULpart.

Special subframes may comprise multiple instances of a DL part, a gap,and a UL part. For example a special subframe may have or may includetwo instances of a DL part, a gap, and a UL part. In an example, atleast one of the DL parts may include a control region. In a furtherexample, all of the DL parts may include a control region.

A special subframe may be used to create a self-contained subframe. Inan example, a self-contained subframe may be a subframe in which a DLgrant and/or DL data may be received, for example, by a WTRU, in a DLpart of the subframe and the HARQ feedback for the DL grant and/or DLdata may be transmitted, for example, by the WTRU, in a UL part of thesubframe. The HARQ feedback may be transmitted on a PUCCH channel in aUL part of the subframe.

In a further example, a self-contained subframe may be a subframe inwhich a UL grant may be received, for example, by a WTRU, in a DL partof the subframe and granted resources may be in a UL part of thesubframe. In another example, a self-contained subframe may be asubframe in which a UL grant may be received, for example, by a WTRU, ina DL part of the subframe and the UL transmission, for example, by theWTRU, may be in a UL part of the subframe.

Examples herein also describe configuring a WTRU with special subframes.A WTRU may also determine when to use a special subframe, for example,for UL transmission such as a PUCCH or PUSCH transmission. For example,a dynamic indication in a grant (such as, for example, a DL grant or aUL grant) may indicate the use of a special subframe (for example, for aPUCCH or a PUSCH transmission), and a WTRU may determine which specialsubframe to use for the UL transmission based on timing, for example,with respect to the grant.

Special subframes may be configured and/or used, for example, for ULtransmission of PUCCH, PUSCH, and/or HARQ feedback. A set of one or morespecial subframe configurations may be provided and/or used. Forexample, the set may be provided via higher layer signaling such as RRCdedicated or broadcast signaling.

A special subframe configuration may indicate one or more of thefollowing for a special subframe: the number of DL, UL, and/or gap partsin the special subframe; the positions or locations of the DL, UL,and/or gap parts within the special subframe; the size of DL, UL, and/orgap parts in the special subframe; an index or other identifier for orassociated with the special subframe configuration; the purpose forwhich one or more DL parts of the special subframe may be used; and/orthe purpose for which one or more UL parts of the special subframe maybe used.

The purpose for which a UL and/or DL part of a special subframe may beused may be indicated, for example, separately, from the specialsubframe configuration.

A configuration (for example, a ConfigSF) may be provided that indicateswhich subframes may be used as special subframes. ConfigSF may indicatea purpose, for example, a UL purpose, for which an indicated subframe(for example, each indicated subframe or all indicated subframes) may beused. A UL purpose may be at least one of HARQ feedback, PUCCHtransmission, PUSCH transmission, and/or SRS transmission. ConfigSF mayindicate the special subframe configuration, for example, by itsidentifier, for one or more (for example, each or all) of the subframesindicated by ConfigSF.

ConfigSF may or may also indicate which subframes may be used as DLsubframes. In an example, ConfigSF may or may also indicate whichsubframes may be completely used as DL subframes. The subframes that maybe indicated as DL subframes may be UL or special subframes inConfigCell.

ConfigSF may be configured via higher layer signaling such as RRCsignaling, broadcast signaling or both. ConfigSF may be configured viaphysical layer signaling such as in a DCI format. The signaling may becell-specific, WTRU-specific, and/or WTRU-group specific. ConfigSF maybe configured and/or updated periodically.

There may be a first ConfigSF that may be signaled, for example, viahigher layer signaling and/or semi-statically. In an example, the firstConfigSF may be a baseline ConfigSF that may be signaled, for example,via higher layer signaling and/or semi-statically. There may be a secondConfigSF that may be signaled dynamically and/or periodically. Thesecond ConfigSF may override the first ConfigSF.

The second ConfigSF may be applicable to and/or valid for a length oftime such as a specific length of time. A WTRU may use at least ConfigSFto determine which subframes may be used at least occasionally asspecial subframes.

A DL and/or UL grant may indicate, for example, to a WTRU, to use aspecial subframe for a UL transmission or for reception of a DLtransmission. The special subframe may be one indicated in ConfigSF. AUL transmission may be or may include transmission of HARQ feedback inthe UL, a PUCCH transmission, and/or a PUSCH transmission. A DLtransmission may be or may include transmission of HARQ feedback in theDL (for example, on a PHICH), a PDCCH and/or EPDCCH transmission, and/ora PDSCH transmission.

For example, a DL grant may indicate whether a special subframe may beused for PUCCH transmission and/or for HARQ feedback (for example, inthe UL and/or on a PUCCH) for the DL transmission. A WTRU may transmit aPUCCH and/or HARQ feedback in a special subframe, for example based onreceiving an indication to use a special subframe for a PUCCH and/orHARQ feedback.

The subframe or special subframe to use, for example for an ULtransmission, a PUCCH transmission, and/or for HARQ feedback, may beindicated, for example to a WTRU, and/or determined, for example by aWTRU, according to one or more of the following: the subframe or specialsubframe may be one indicated in ConfigSF; which subframe to use as aspecial subframe may be indicated in the DL grant; the special subframemay be a subframe indicated as an MBSFN subframe, for example, inConfigCell; the special subframe may be the next special subframe thatsatisfies a criteria or the next special subframe indicated in ConfigSFthat satisfies a criteria where the criteria may be that the start ofthe special subframe or a portion (for example, a UL portion) of thespecial subframe exceeds a threshold amount of time (for example, insubframes, TTIs, symbols, time samples, timeslots, and the like) afterthe time (for example, subframe, TTI, symbol, time samples, timeslot,and the like) in which the DL grant or DL data is received; the specialsubframe that may be used may begin at least a number of, for example,n, TTIs after the subframe in which the DL grant or DL data is received;the UL portion of the special subframe that may be used may be in atimeslot that begins at least a number (for example, n) TTIs after thestart of the timeslot in which the DL data is received; the specialsubframe may be the same subframe as the subframe in which the DL grantis received, for example, the current special subframe; the specialsubframe may be the current special subframe, for example if the currentspecial subframe satisfies a criteria where the criteria may be that thestart (or a part of) of a UL portion of the current special subframeexceeds a threshold amount of time (for example, in TTIs, symbols, timesamples, timeslots, and the like) after the time (for example, TTI,symbol, time samples, timeslot, and the like) in which the DL grant orDL data is received; and/or the UL portion of the current specialsubframe may be used, for example, when the UL portion may begin atleast a number of, for example, n, TTIs, symbols, and/or time samplesafter the time in which the DL grant or DL data is received.

A time unit of a TTI may be in at least one of subframes, TTIs, symbols,time samples, and/or timeslots. The DL grant may indicate the specialsubframe configuration of the special subframe that may be used forPUCCH and/or HARQ feedback.

A special subframe may be used for transmission of a PUCCH and/or HARQfeedback. If a WTRU receives an indication, for example, in a DL grant,that a special subframe may be used for PUCCH transmission and/or HARQfeedback (for example, in the UL and/or on a PUCCH), the WTRU maytransmit PUCCH and/or HARQ feedback in a special subframe. The specialsubframe may be a special subframe as described herein. For example, thespecial subframe may be one indicated in ConfigSF. The special subframemay be the next special subframe that satisfies a criteria or the nextspecial subframe indicated in ConfigSF that satisfies a criteria. Thecriteria may be as described above. The special subframe may be thecurrent special subframe, for example, if the current special subframesatisfies a criteria such as one described herein.

As used in the examples herein, substitution and switched may be usedinterchangeably. In an example, special subframes may be substituted forUL and/or DL subframes, for example to send HARQ feedback. Accordingly,in an example, a UL and/or DL subframe may be switched to a specialsubframe. In another example, two DL subframes may be switched tospecial subframes. In a further example, two UL subframes may beswitched to a special subframes. In still further examples, more thantwo UL and/or DL subframes may be switched to special subframes. In anexample, one or more subframes switched to special subframes may then beused to send HARQ feedback. Further, substitution may be viaconfiguration that may be broadcast, WTRU specific, and/or WTRU-groupspecific. Configuration may be by an eNode-B or cell. Configuration maybe via physical layer signaling such as in a DCI format. Configurationmay be via higher layer signaling such as RRC signaling or broadcastsignaling.

The WTRU may transmit the PUCCH and/or the HARQ feedback in a UL portionof the special subframe, for example, according to the special subframeconfiguration of that subframe. The location of the PUCCH and/or HARQfeedback, for example, in time and/or frequency, may be a function ofthe TTI, the location of the DL grant and/or the location of the DL datatransmission.

For a special subframe in which it may transmit the PUCCH and/or HARQfeedback, the WTRU may use the special subframe configuration itreceived, for example, in higher layer signaling, ConfigSF, theassociated DL grant, and/or other ways such as those described inexamples herein. If a WTRU receives an indication, for example, in a DLgrant, that a special subframe may be used for PUCCH transmission and/orHARQ feedback (for example, in the UL and/or on a PUCCH), the WTRU maymonitor, attempt to receive and/or receive a DL transmission in a DLpart of the special subframe in which it may transmit the PUCCH and/orHARQ feedback.

FIG. 5B is a diagram illustrating an example of sending HARQ feedback ona switched special subframe in a configuration supporting an sTTI. Asshown in an example in FIG. 5B, when using a legacy TTI with a TDD UL/DLsubframe configuration, DL data may be received by a WTRU on a DLsubframe, such as subframe 520. The TTI and the subframe may be the samelength in time, such as 1 ms. The TDD UL/DL subframe configuration maybe TDD UL/DL subframe configuration 2, in an example. The WTRU may thensend HARQ feedback for subframe 520 on a UL subframe, such as subframe530. In another example shown in FIG. 5B, a subframe such as subframe520 may correspond to one legacy TTI and two sTTIs such as sTTIs 540 and541. DL data may be received by a WTRU for an sTTI such as sTTI 540. TheWTRU may then send HARQ feedback for the sTTI 540 on an sTTIcorresponding to a UL subframe, such as sTTI 560 corresponding to ULsubframe 530. Two is used as a non-limiting example of the number ofsTTIs that may correspond to a subframe and/or to a legacy, long, ornormal TTI. The WTRU may not send HARQ feedback for the sTTI 540 on aspecial subframe such as special subframe 557, for example since the ULpart 558 of the special subframe 557, which may be a legacy specialsubframe, may not be long enough to support HARQ feedback transmission.

In order to improve latency, a WTRU may switch DL subframes to bespecial subframes. In an example shown in FIG. 5B, DL subframe 525 whichcorresponds to DL sTTI 550 and 555 may be switched to special subframe580. Special subframe 580 may include at least a UL part 585 and a gappart 583. DL data may be received by the WTRU for an sTTI, such as sTTI570. The WTRU may then send HARQ feedback for sTTI 570 on the UL part585 of special subframe 580. As can be seen in FIG. 5B, latency can beimproved in this way because the WTRU may send HARQ feedback on the ULpart 585 of special subframe 580 sooner than the WTRU may send HARQfeedback in UL sTTI 560. As further shown in an example in FIG. 5B, theHARQ feedback may be sent in the nearest UL location, for example thenearest UL location that may support HARQ feedback transmission, atleast four sTTIs after the receipt of the corresponding DL data.

A PUSCH transmission may use a special subframe. The examples describedherein utilizing a special subframe for PUCCH transmission may beapplied to utilizing a special subframe for PUSCH transmission. Forexample, DL grant when referring to PUCCH transmission described hereinmay be replaced by UL grant for referring to PUSCH transmission.

For example, a UL grant may indicate whether a special subframe may beused for PUSCH transmission. The special subframe may be the nextspecial subframe that satisfies a criteria or the next special subframeindicated in ConfigSF that satisfies a criteria. The criteria may be asdescribed for PUCCH transmission with UL grant substituted for DL grant.

For example, the criteria may be that the start of the special subframeor a portion (for example, a UL portion) of the special subframe exceedsa threshold amount of time (for example, in subframes, TTIs, symbols,time samples, timeslots, and the like) after the time (for example,subframe, TTI, symbol, time samples, timeslot, and the like) in whichthe UL grant is received.

The special subframe may be the same subframe as the subframe in whichthe UL grant is received (for example, the current special subframe).The special subframe may be the current special subframe, for example,if the current special subframe satisfies a criteria. The criteria maybe as described for PUCCH transmission with UL grant substituted for DLgrant.

For example, the criteria may be that the start (or a part of) of a ULportion of the current special subframe exceeds a threshold amount oftime (for example, in TTIs, symbols, time samples, timeslots, and thelike) after the time (for example, TTI, symbol, time samples, timeslot,and the like) in which the UL grant is received.

If a WTRU receives an indication, for example, in a UL grant, that aspecial subframe may be used for PUSCH transmission, the WTRU maytransmit PUSCH in a special subframe. The special subframe may be aspecial subframe as described herein. For example, the special subframemay be the next special subframe that satisfies a criteria or the nextspecial subframe indicated in ConfigSF that satisfies a criteria. Thecriteria may be as described above. The special subframe may be thecurrent special subframe, for example, if the current special subframesatisfies a criteria such as one described herein.

The WTRU may transmit the PUSCH in a UL portion of the special subframe,for example, according to the special subframe configuration of thatsubframe. The location of the PUSCH, for example, in time and/orfrequency, may be a function of the TTI and/or the location of the ULgrant. If a WTRU receives an indication, for example, in a UL grant,that a special subframe may be used for PUSCH transmission, the WTRU maymonitor, attempt to receive and/or receive a DL transmission in a DLpart of the special subframe in which it may transmit the PUSCH. Whenusing a special subframe for PUSCH transmission, the HARQ feedback inthe DL, for example, from the eNode-B, may be provided in a DL subframeor a DL portion of a special subframe according to a configuration or arule. The UL grant (or other information in the DCI format that maycontain the UL grant) may include or identify the configuration or ruleto use. WTRU retransmission, for example, if a NACK or no ACK isreceived, may be according to a configuration or a rule. Theconfiguration or the rule may be indicated in or with the UL grant.

A PUCCH transmission may use special subframe UL symbols. For example, aPUCCH transmission may use special subframe UL symbols and/or timesamples that may correspond to UpPTS symbols of the special subframe ora UpPTS part of the special subframe. For example, a special subframemay include or may end with a number of symbols (for example, NSsymbols) that may be UL symbols or UpPTS symbols. The number of symbols(which may be described as the length in symbols) may be 1 or 2, forexample, as shown in FIG. 4 under UpPTS. One or more of the NS symbol(s)may be used (for example, typically used or reserved) for SRStransmission. SRS transmissions may be triggered by an eNode-B. SRStransmissions may be used for UL channel measurements, for example,occasional UL channel measurements. The resources available in the NSsymbols may not be used, for example, at least sometimes. The resourcesavailable in the NS symbols may be utilized to create additional PUCCHtransmission opportunities in a TDD special subframe, for example, shortor shortened PUCCH (sPUCCH) transmission opportunities. The sPUCCHtransmission opportunities in a special subframe configuration may beindependent of the special subframe configuration. sPUCCH transmissionopportunities may be used for HARQ feedback, for example, to reduce RTTlatency.

An sPUCCH may, for example, be used when the symbols available for ULtransmission are fewer than used by a legacy PUCCH. In an example, ansPUCCH may be used when an UL sTTI is used for transmitting UL controlinformation such as HARQ feedback. In another example, the UL symbolsavailable in a special subframe may be limited to a number, for exampleto 1 or 2 symbols, which may be too short for a legacy PUCCH design. Asa result, an sPUCCH may be used instead.

FIG. 6 is a diagram illustrating an example of HARQ feedback latencywith and without sPUCCH transmission in UpPTSs of special subframes. Asshown in an example in diagram 600, TDD UL/DL configuration 2 may beused with legacy PUCCH transmission 610 and with sPUCCH transmission inUpPTS 660. sPUCCH transmission may be allowed in a special subframe, forexample, in a UpPTS of a special subframe. HARQ feedback may betransmitted using a sPUCCH. In this example, latency between DLreception and HARQ feedback transmission may be reduced by 1 subframe orTTI for at least some instances of PDSCH reception (for example,instances with HARQ feedback delay>4 subframes or TTIs). In the exampleshown in FIG. 6, k may be the time distance in number of subframesbetween a PDSCH and its corresponding HARQ feedback. Using sPUCCH in aspecial subframe (for example, in a UpPTS), the average k may be reducedfrom 6.25 subframes or TTIs to 5.5 subframes or TTIs.

In an example shown in FIG. 6, under TDD UL/DL configuration 2 used withlegacy PUCCH transmission 610, the WTRU may receive a PDSCH 620 in DLsubframe 0 and a PDSCH 630 in special subframe 1. The WTRU may thentransmit HARQ feedback for the PDSCHs, such as an ACK or a NACK, in thenext available UL subframe more than 4 subframes after the receipt ofthe PDSCH, which may be UL subframe 7. In this way, the WTRU maytransmit an ACK or a NACK 625 for PDSCH 620 and an ACK or a NACK 635 forPDSCH 630 in UL subframe 7.

Further, under TDD UL/DL configuration 2 used with sPUCCH transmissionin UpPTS 660, the WTRU may receive a PDSCH 670 in DL subframe 0 and aPDSCH 680 in special subframe 1. The WTRU may then transmit HARQfeedback, such as an ACK or a NACK, in the next available specialsubframe or UL subframe more than 4 subframes after the receipt of thePDSCH, which may be special subframe 6. In this way, the WTRU maytransmit an ACK or a NACK 675 for PDSCH 670 and an ACK or a NACK 685 forPDSCH 680 in special subframe 6. As a result, the feedback delay may bereduced by 1 subframe by using sPUCCH transmission in UpPTS 660 insteadof legacy PUCCH transmission 610.

For sPUCCH transmission on (or at least on) SRS resources, a WTRU may beconfigured with a set of parameters. In an example, the parameters maybe or may include the set of parameters defined, configured, and/or usedfor SRS. In a further example, the parameters may be or may include asubset of the set of parameters defined, configured, and/or used forSRS. The parameters may include information regarding the location ofthe resources or information from which the location information may bedetermined. The location information may include the frequencyresources, the bandwidth, and/or the resource blocks (RBs). SRS mayinclude periodic and/or aperiodic SRS. SRS may include SRS of triggertype 0 and/or type 1. The set of parameters may be or may include one ormore parameters that may be independent of the SRS (type 0 and/ortype 1) parameters. For example, the set of parameters may be or mayinclude all of the parameters that may be independent of the SRS (type 0and/or type 1) parameters.

Multiple sets of parameters may be configured and/or used. Separateparameters may be configured for and/or used by different WTRUs orgroups of WTRUs. There may be a number of (for example, three) sets ofparameters, that may, for example, be the same as the number of (forexample, three) sets of parameters configured for SRS trigger type 1and/or DCI Format 4. Which set of parameters a WTRU may use may beconfigured or indicated semi-statically (for example, by higher layersignaling) or dynamically (for example, by physical layer signaling).

The availability of special subframe resources for sPUCCH transmissionmay be configured, indicated, and/or granted through higher layersignaling or physical layer signaling (for example, via a DL controlchannel or DCI format). Special subframe resource availability maybecome effective immediately in the same subframe as the indication orin a later special subframe, for example, the next special subframe orthe next special subframe that may be used for sPUCCH. Special subframeresources may be or may include UL symbols or resources, UpPTS symbolsor resources, and/or SRS symbols or resources.

The availability and/or use of special subframe resources for sPUCCHtransmission may be a function of the frame configuration (for example,the TDD UL/DL configuration). For example, special subframe resourcesmay be available and/or used for sPUCCH transmission for all or a subsetof PDSCH reception events. Special subframe resources may be availableand/or used for sPUCCH transmission for all or a subset of PDSCHreception events for which their corresponding HARQ feedback mayexperience a long delay (for example, greater than 4 or 5 subframes).The delay may be a function of the frame configuration. The WTRU maydetermine the availability or unavailability of resources (for example,special subframe resources) for sPUCCH transmission without requiringany additional signaling. For example, for UL/DL configuration 2 shownin FIG. 6, availability and/or use of special subframes may apply (forexample, may only apply) to HARQ feedback for PDSCH 640, 690 receptionin subframe 4 and PDSCH 650, 691 reception in subframe 9. Using legacyPUCCH, PDSCH 640, 650 reception in subframes 4 and 9 may experience thelongest delay for HARQ feedback, such as for HARQ feedback 645 and HARQfeedback 655, respectively. Using sPUCCH, PDSCH 690, 691 reception insubframes 4 and 9 may experience a shorter delay for HARQ feedback, forexample by 1 subframe or 1 ms, such as for HARQ feedback 695 and HARQfeedback 696, respectively.

SRS may be configured to span over a multiple of a number of RBs (forexample, 4 RBs) in frequency. Further, SRS may be configured to spanover any multiple of a number of RBs in frequency. The sPUCCH may span a(for example, any) multiple of the number of RBs (for example, 4 RBs)that may be allowed by an SRS configuration. The SRS bandwidth may beconfigured as large as needed for transmission of the sPUCCH, forexample, in case of availability of a single UL symbol in a givenconfiguration. The transmitted sPUCCH blocks may be rate-matched orrepeated over several RBs, for example, to achieve higher coding gain.

An sPUCCH transmission may be transmitted simultaneously with an SRStransmission. The SRS mapping may be done on a subset of subcarriers(for example, every second subcarrier). The unused resources may be usedto carry the sPUCCH. The sPUCCH transmission may not be accompanied withan (for example, any) UL DMRS, for example, since the SRS may be usedfor channel estimation for PUCCH demodulation. Some of the SRS power maybe shifted to the sPUCCH, for example, in case of simultaneoustransmission of SRS and sPUCCH. The shift may improve performance.

WTRUs may use MBSFN subframes as special subframes. In an example, MBSFNsubframes may be used as special subframes by at least some WTRUs, forexample in a cell. Configuring DL subframes that may be used as specialsubframes as MBSFN subframes may enable backwards compatibility withlegacy WTRUs when DL subframes are used as special subframes. A WTRU mayreceive a configuration or indication as to which MBSFN subframes may beused as special subframes.

In the examples described herein, the terms MBSFN subframe may besubstituted for the terms special subframe and vice versa, and still beconsistent with the examples provided herein.

Some WTRUs, for example, legacy WTRU s may not expect a DL grant, DLdata, and/or CRS in an MBSFN subframe. MBSFN subframes may be used forUL transmission, for example, in regions of the subframe not used for DLcontrol. MBSFN subframes may be used for UL transmission, for example,without impacting legacy WTRUs.

Some WTRUs (for example, LTE R10 WTRUs) may blind decode for a DLcontrol channel in an MBSFN subframe, but may not expect CRS in the dataregion of an MBSFN subframe (for example, if the WTRU does not receive agrant in the subframe). MBSFN subframes may be used for UL transmission,for example, without impacting WTRUs such as these.

A WTRU may monitor and/or receive a DL control channel in an MBSFNsubframe. The DL control channel may indicate whether the MBSFN subframemay be used as a DL subframe or a special subframe.

A WTRU may receive an indication in a UL grant and/or DL grant as towhether an upcoming (or the current) MBSFN subframe may be used as aspecial subframe and/or for UL transmission. If the WTRU determines thatan upcoming (or the current) MBSFN subframe may be used as a specialsubframe and/or for UL transmission, the WTRU may determine which MBSFNsubframe according to a criteria. If the WTRU determines that anupcoming (or current) MBSFN subframe may be used as a special subframeand/or for UL transmission, the WTRU may make the UL transmission inthat subframe.

For example, a DL grant may indicate whether an MBSFN subframe may beused as a special subframe. A DL grant may be used to indicate whetheran MBSFN subframe may be used for PUCCH transmission and/or for HARQfeedback (for example, in the UL and/or on a PUCCH) for the DLtransmission. If a WTRU determines that an MBSFN subframe may be usedfor PUCCH transmission and/or for HARQ feedback, for example, based onan indication in a DL grant, the WTRU may transmit the PUCCH and/or HARQfeedback in the determined subframe.

The following example procedures may be used under the design for usingMBSFN subframes as special subframes. For example, which MBSFN subframeto use may be indicated in the DL grant. Also, the DL grant and/or otherconfiguration may indicate the special subframe configuration for theMBSFN subframe. In another example, the MBSFN subframe may be thecurrent or next MBSFN subframe that satisfies a criteria. The criteriamay be that the start of the MBSFN subframe or a portion (for example, aUL portion) of the MBSFN subframe (for example, according to the specialsubframe configuration for the MBSFN subframe) exceeds a thresholdamount of time after the time in which the DL grant or DL data isreceived. The threshold amount of time may be expressed, for example, insubframes, TTIs, symbols, time samples, timeslots, and the like. Thetime in which the DL grant or DL data is received may be expressed, forexample, in subframes, TTIs, symbols, time samples, timeslots, and thelike.

In a further example, the MBSFN subframe that may be used may begin atleast a number of, for example, n, TTIs after the subframe in which theDL grant or DL data is received. In an additional example, the ULportion of the MBSFN subframe (for example, according to the specialsubframe configuration for the MBSFN subframe) that may be used may bein a timeslot that begins at least a number (for example, n) TTIs afterthe start of the timeslot in which the DL data is received.

Further, the MBSFN subframe may be the current special subframe, forexample if the current MBSFN subframe satisfies a criteria. The criteriamay be that the start (or a part of) of a UL portion of the currentMBSFN subframe (for example, according to the special subframeconfiguration for the MBSFN subframe) exceeds a threshold amount of timeafter the time in which the DL grant or DL data is received. Thethreshold amount of time may be expressed, for example, in subframes,TTIs, symbols, time samples, timeslots, and the like. The time in whichthe DL grant or DL data is received may be expressed, for example, insubframes, TTIs, symbols, time samples, timeslots, and the like. Instill another example, the UL portion of the current special subframemay be used, for example, when the UL portion may begin at least anumber of, for example, n, TTIs, symbols, and/or time samples after thetime in which the DL grant or DL data is received.

The examples described herein for PUCCH transmission, for example, in asubframe configured as an MBSFN subframe, may be applied to PUSCHtransmission, for example, in a subframe configured as an MBSFNsubframe. In the examples, DL grant may be replaced by UL grant withoutloss of functionality.

Examples of UL channel design for special subframes and variable size ULtransmission regions are provided herein. In particular, examples of adesign of PUCCH and PUSCH for variable size UL regions for transmission,for example, as a function of the size of the UL region, are provided. APUCCH and/or PUSCH may be designed according to a time that may beavailable for the transmission of the channel. The design of a channelmay include the allocation of resources in time and/or frequency.

For example, a PUCCH and/or PUSCH in a special subframe may be designedaccording to at least one of the number of time samples, symbols,physical resource blocks (PRBs), and/or resource elements (REs) in (oravailable in) the UL portion of the special subframe. Further, a PUCCHand/or PUSCH in another time span may be designed according to at leastone of the number of time samples, symbols, physical resource blocks(PRBs), and/or resource elements (REs) in (or available in) the ULportion of the other timespan.

A PUCCH and/or PUSCH in a special subframe may be designed according toat least one of the number of time samples, symbols, PRBs, and/or REsavailable for the UL transmission in the special subframe. Further, aPUCCH and/or PUSCH in another time span may be designed according to atleast one of the number of time samples, symbols, PRBs, and/or REsavailable for the UL transmission in the other time span.

A PUCCH and/or PUSCH in a special subframe may be designed according toat least one of the frequency location of the PRBs, and/or REs availablefor the UL transmission in the special subframe. Further, a PUCCH and/orPUSCH in another time span may be designed according to at least one ofthe frequency location of the PRBs, and/or REs available for the ULtransmission in the other time span.

The design parameters of a PUCCH may include one or more of thefollowing characteristics of the PUCCH: the frequency location; the TTI;the number of REs; the number of PRBs; the use of frequency hopping;and/or the starting symbol, time sample, or other time unit, for examplewithin the subframe. The design parameters of a PUSCH may include one ormore of the following characteristics of the PUSCH: the TTI; the use offrequency hopping; the starting symbol, time sample, or other time unit,for example within the subframe; the location of a UL reference signal(RS) (for example, a demodulation reference signal (DM-RS)); and/ortransport Block Size (TBS).

One or more of the design parameters of the PUCCH and/or PUSCH in aspecial subframe may be based on or a function of the configuration of aspecial subframe, for example, the configuration of the special subframein which the PUCCH and/or PUSCH may be or may be intended to betransmitted. A WTRU may determine one or more of the design parametersof the PUCCH and/or PUSCH in a special subframe based on or as afunction of the configuration of a special subframe.

The configuration of a special subframe may include at least one of: thesize of the DL portion in terms of times samples, symbols, and/or othertime units; the size of the UL portion in terms of times samples,symbols, and/or other time units; and/or the size of the gap in terms oftimes samples, symbols, and/or other time units.

The configuration of a special subframe may include the allocation ofPUCCH resources in the special subframe. For example, the configurationof a special subframe may include the allocation of PUCCH resources inone or more UL portions of the special subframe.

In an example, a subframe may have a number of symbols S1 available forUL transmission such as PUCCH and/or PUSCH transmission. The subframemay be configured and/or determined to occupy or be allocated C1subcarriers. Another subframe may have a number of symbols S2 availablefor UL transmission such as PUCCH and/or PUSCH transmission. Thesubframe may be configured and/or determined to occupy or be allocatedC2 subcarriers. If S1<S2, then C1 may be greater than C2. Another timeunit such as time samples or timeslots may be substituted for symbols inthe examples described herein. More symbols for UL transmission maycorrespond to fewer subcarriers or REs for UL transmission.

A WTRU may be configured with a PUCCH allocation based on a number ofsymbols being allocated for the PUCCH. This may be a base PUCCHallocation. A WTRU may determine the PUCCH allocation in a subframe witha number (for example, a different number) of symbols allocated for thePUCCH based on the base PUCCH allocation. The base allocation may use S1symbols and C1 carriers. The WTRU may determine the allocation foranother subframe that may use S2 symbols. The allocation for the othersubframe may include the number of subcarriers, for example, C2, and/orthe location of the allocation in frequency. The allocation for theother subframe may be determined as a function of at least one of S1,S2, C1, and/or the frequency location of the base allocation.

In the embodiments and examples described herein, PUSCH may besubstituted for PUCCH and vice versa and still be consistent with theexamples provided herein. It will also be appreciated that anycombination of the disclosed features/elements may be used in one ormore of the embodiments and examples.

FIG. 7A is a diagram illustrating an example of transmitting HARQfeedback on a PUCCH in a UL portion in determined resources of adetermined special subframe with a determined special subframeconfiguration. As shown in an example in FIG. 7A, a WTRU may receive atime division duplex (TDD) uplink (UL)/downlink (DL) subframeconfiguration 710. Further, the WTRU may receive a DL grant with anindication to use a special subframe for PUCCH transmission 715. TheWTRU may then dynamically determine which subframe to switch to aspecial subframe and may switch the subframe to a special subframe 720.Further, the WTRU may determine a special subframe configuration to usefor the determined special subframe 725. Also, the WTRU may determineresources of the determined special subframe to use for a PUCCH 730.

The WTRU may then determine PUCCH resources and PUCCH design parametersfor the PUCCH 735. Further, the WTRU may transmit HARQ feedback on thePUCCH in a UL portion in the determined resources of the determinedspecial subframe with the determined special subframe configurationusing the determined PUCCH resources and PUCCH design parameters 740.

In an example, the WTRU may also receive DL data in a DL subframe. TheWTRU may then transmit the HARQ feedback in the determined specialsubframe at least four sTTIs after the DL subframe.

In examples provided herein, an LTE guard-band may be used.Specifically, a guard-band may be configured for, determined for usefor, and/or used for UL resources and/or DL resources. A guard-band maybe configured for, determined for use for, and/or used for HARQ feedbacktransmission in the UL and/or DL. A guard-band may be configured for,determined for use for, and/or used for UL resources and/or DL resourcesfor HARQ feedback transmission.

The terms HARQ feedback, HARQ-ACK, HARQ indication, and ACK/NACKindication may be used interchangeably herein. Furthermore, aguard-band, a secondary carrier, extended carrier, and a secondfrequency band may be used interchangeably herein.

FIG. 7B is a diagram illustrating an example of a guard-band PRBconfiguration for HARQ feedback. As shown in an example in diagram 700,PRB 760 and PRB 770 in guard-band A and PRB 780 and PRB 790 inguard-band B may be configured and/or used. The use of a guard-band PRBconfiguration and/or of guard-band PRBs may not be limited to HARQfeedback transmission.

In examples provided herein, a guard-band PRB configuration may beprovided and/or used. A PRB in a guard-band may be referred to as G-PRBand a PRB in a system bandwidth may be referred to as S-PRB. The termsPRB, PRB-pair, and RB may be used interchangeably and still beconsistent with the examples provided herein.

A set of G-PRBs may be near or adjacent (for example, in frequency orPRB) to a set of S-PRBs. In an example, the number of S-PRBs may bedetermined based on an indication from a broadcasting channel (forexample, a master information block (MIB), or a SIB) and the number ofG-PRBs may be determined based on at least one of following: anindication from a higher layer signaling; one or more system parameters(for example, physical cell-ID, system bandwidth and the like); and/orcarrier frequency.

One or more G-PRBs may be used for a certain transmission scheme (ormode) configuration. For example, if a WTRU is configured with ashort-TTI transmission scheme (or mode), then G-PRBs may be used. Thehigher layer signaling for a short-TTI transmission scheme may includefull or partial configuration information for G-PRBs.

Based on the physical cell-ID (PCI) detection from a synchronizationchannel, and/or one or more system parameters acquired from abroadcasting channel, the G-PRB configuration may be determined, forexample, by a WTRU.

One or more G-PRBs may be located next to the lowest S-PRB index,highest S-PRB index, or both lowest and highest S-PRB indices.

In examples provided herein a TDD subframe configuration may be providedand/or used for guard-band PRBs. In an example, a TDD configuration (forexample a UL/DL subframe configuration) for S-PRBs and for one or moreG-PRBs may be independently configured. In another example, the TDDconfiguration for G-PRB(s) may be determined based on the TDDconfiguration for S-PRBs.

FIG. 8 is a diagram illustrating an example of a TDD configuration forG-PRBs based on a TDD configuration for S-PRBs. In an example shown indiagram 800, a first TDD configuration 810 may be used for S-PRBs and asecond TDD configuration 860 may be used for G-PRB(s), or vice versa.The first TDD configuration 810 may, for example, be TDD UL/DLconfiguration 0, for example per an indication received by the WTRU. Thefirst and second TDD configurations may be indicated with an offset. Forexample, the first TDD configuration may be indicated from abroadcasting channel (for example, a MIB) which may be transmitted inone or more S-PRBs, and the second TDD configuration may be indicated asan offset from the first TDD configuration.

The second TDD configuration 860 may be determined based on the firstTDD configuration 810. As a result, one or more of following examplesmay apply. For DL subframes or UL subframes, an opposite directionsubframe may be used in the second TDD configuration based on the firstTDD configuration. For example, if a subframe n is a DL subframe in thefirst TDD configuration, the subframe n is a UL subframe in the secondTDD configuration. As shown in an example in FIG. 8, DL subframes 811,816 in the first TDD configuration 810 may be used as UL subframes 861,866 in the second TDD configuration 860. Also, UL subframes 813, 814,815, 818, 819, 820 in the first TDD configuration 810 may be used as DLsubframes 863, 864, 865, 868, 869, 860 in the second TDD configuration860. In another example, a special subframe for a subframe n in thefirst TDD configuration may be replaced by a UL subframe in the secondTDD configuration. In an additional example, a special subframe for asubframe n in the first TDD configuration may be used as a specialsubframe in the second TDD configuration. For example, special subframes812, 817 in the first TDD configuration 810 may be used as specialsubframes 862, 867 in the second TDD configuration 860. Further, one ormore special subframe properties may be different for the first TDDconfiguration and the second TDD configuration (for example, DwPTS,UpPTS, and/or Gap). The UL part of the special subframe in the secondTDD configuration may have a larger number of uplink symbols (forexample, SC-FDMA symbols) than the UL part of the special subframe inthe first TDD configuration.

FIG. 9 is a diagram illustrating an example of timing offset betweenS-PRBs and G-PRBs. In an example shown in diagram 900, the timing of aTDD subframe for G-PRB(s) 960 may be determined, configured, orindicated based on the timing of a TDD subframe for S-PRB(s) 910.

A timing offset (Toffset) may be used to determine or configure thetiming of G-PRB(s) 960, for example the timing of a subframe for G-PRBs,based on the timing of S-PRB(s) 910, for example the timing of asubframe for S-PRBs. The timing offset may be determined or configuredby one or more of the following examples. Toffset may be determinedbased on the processing time of the short-TTI. The processing time ofthe short-TTI may be indicated in at least one of a broadcastingchannel, higher layer signaling, and a WTRU capability indication.Toffset may be determined based on the short-TTI length. If a short-TTIlength is Nshort [ms], the Toffset may be Nshort×Noffset [ms]. In anexample, Toffset may be configured by higher layer signaling. In afurther example, Toffset may be larger than a subframe length, such as,for example, 1 ms. In another example, Toffset may be blindly detectedby a WTRU. For example, a synchronization signal may be transmitted inG-PRB(s) in a predefined time location. A WTRU may use a synchronizationsignal transmitted in G-PRBs and, optionally, a synchronization signaltransmitted in S-PRBs to determine Toffset.

In examples provided herein, HARQ feedback may use guard-band PRBs. APUSCH, a PDSCH or both may be transmitted in S-PRBs and the associatedHARQ feedback may be transmitted in G-PRBs.

One or more G-PRB(s) may be used for PUCCH transmission that may forexample carry or include HARQ feedback that may be associated with aPDSCH transmission in S-PRB(s). Further, one or more G-PRB(s) may beused for EPDCCH transmission that may for example carry or include HARQfeedback that may be associated with a PUSCH transmission in S-PRB(s).The terms EPDCCH, machine-type communications (MTC) PDCCH (M-PDCCH),short PDCCH (S-PDCCH), and narrowband PDCCH (NB-PDCCH) may be usedinterchangeably herein. HARQ feedback associated with one or more ULtransmissions may be transmitted via an E-PDCCH. For example, a DCI witha group radio network temporary identifier (RNTI) may be transmitted,where the DCI may carry HARQ feedback associated with one or more ULtransmissions. One or more G-PRB(s) may be used for PDSCH transmissionthat may for example carry or include HARQ feedback which may beassociated with a PUSCH transmission in S-PRBs.

FIG. 10 is a diagram illustrating an example of a HARQ feedback resourcedetermination. A subset of subframes in G-PRB(s) may be used for HARQfeedback based on the HARQ feedback resource availability in S-PRB(s).For example, for a PDSCH (or a PUSCH) transmission, if an associatedHARQ feedback resource is available in S-PRB(s) within a certain timewindow, the HARQ feedback corresponding to the PDSCH transmission may betransmitted in S-PRB(s). Otherwise, the associated HARQ feedback may betransmitted in G-PRB(s).

The certain time window may be predefined. For example, if a PDSCH istransmitted using S-PRB(s) in a subframe n and an HARQ feedback resourceis available in S-PRB(s) at the subframe n+k, the associated HARQfeedback may be transmitted in S-PRB(s). If a HARQ feedback resource isnot available in S-PRB(s) at the subframe n+k, the associated HARQfeedback may be transmitted in G-PRB(s). Here, k may be a positiveinteger number. In addition, the certain time window may be determinedbased on a TTI length, for example a short TTI length. In an example indiagram 1000, k may be 1. As shown in diagram 1000, a WTRU may receiveand/or use a TDD UL/DL subframe configuration for S-PRB(s) 1010. Theconfiguration may, for example, be TDD UL/DL configuration 0, forexample, per an indication received by the WTRU. Further, the WTRU maytransmit HARQ feedback associated with the S-PRB(s) in G-PRB(s) 1060. AWTRU may receive a PDSCH in S-PRBs in a DL subframe such as DL subframe1015. The S-PRB subframe that is 1 subframe after the DL subframe 1015may be a special subframe 1020 that may not have enough UL resources tocarry HARQ feedback. The WTRU may transmit the HARQ feedback associatedwith S-PRB DL subframe 1015 in G-PRB UL subframe 1050. In anotherexample, a WTRU may transmit a PUSCH in S-PRB UL subframe 1030 and mayreceive HARQ feedback associated with that transmission in S-PRB DLsubframe 1040, for example since a DL subframe 1040 is available 1subframe after UL subframe 1030. The WTRU may receive a PDSCH in S-PRBDL subframe 1040 and may transmit the HARQ feedback associated with thatDL transmission in G-PRB subframe 1080, for example since the subframethat is 1 subframe after DL subframe 1040 may be a special subframe 1070that may not have enough UL resources to carry HARQ feedback.

In another example, the HARQ feedback resource may be (implicitly orexplicitly) indicated in an associated downlink control channel whichmay be used for a PDSCH or a PUSCH scheduling. For example, two types ofHARQ feedback resources may be used, predefined, or configured and oneof the HARQ feedback resource types may be indicated in the associateddownlink control channel.

For example, a first type of HARQ feedback resource may be a HARQfeedback resource which may be located or transmitted in S-PRB(s), and asecond type of HARQ feedback resource may be a HARQ feedback resourcewhich may be located or transmitted in G-PRB(s). The type of HARQfeedback resource may be determined based on one or more of an RNTI usedfor the downlink control channel, an (enhanced) control channel element((E)CCE) index used, and/or a PRB index used. The type of HARQ feedbackresource may also be indicated in the DCI.

In an example, a subset of subframes may be used for an sTTItransmission in S-PRB(s) and a corresponding subset of subframes inG-PRB(s) that may be used for HARQ feedback, for example for HARQfeedback transmission, may be determined based on the subset ofsubframes used in S-PRB(s) for an sTTI transmission.

The subset of subframes used for an sTTI transmission in S-PRB(s) may beknown to an eNode-B and/or a WTRU. For example, the subset of subframesfor sTTI may be predetermined based on the TDD subframe configuration.The subset of subframes for sTTI may be indicated in a broadcastingchannel. The subset of subframes for sTTI may be configured in aWTRU-specific manner via higher layer signaling.

Examples using HARQ buffer and process handling are described herein,including DL HARQ processing and UL HARQ processing. For example, HARQprocessing may apply in the DL. A HARQ entity may direct HARQinformation and associated TBs received on a shared channel (forexample, a DL shared channel (DL-SCH)) to the corresponding HARQprocesses, for example, at the WTRU in the DL. At least one TB may beexpected for a TTI or subframe. For example, one TB may be expected whenthe physical layer is not configured for spatial multiplexing (forexample, DL spatial multiplexing). One or two TBs may be expected whenthe physical layer is configured for spatial multiplexing (for example,DL spatial multiplexing). A TB may be received on a PDSCH.

The HARQ process associated with a TTI and/or transmission (for example,DL transmission) may be indicated (for example, by the eNode-B) and/orreceived (for example, by a WTRU) in the received resource grant (forexample, a received DL grant). The terms grant, resource grant, andassignment may be used interchangeably herein.

HARQ processing may apply in the UL. A HARQ entity may identify the HARQprocess(es) for which a UL transmission should take place, for example,at a TTI such as a TTI for which a UL grant is indicated. A HARQ entitymay route one or more of the following information to the appropriateHARQ process(es): received HARQ feedback (for example, ACK/NACKinformation), modulation and coding scheme (MCS) and/or resource(s), forexample, time/frequency resource(s) for transmission. At least some ofthe information may be received from the physical layer. At least someof the information may be received in a UL grant, for example, the ULgrant associated with the UL transmission. HARQ feedback may beapplicable to synchronous UL HARQ. HARQ feedback may not be applicablefor some UL HARQ such as asynchronous UL HARQ.

A HARQ process associated with a TTI and/or for which a transmission mayor should take place may be indicated (for example, by the eNode-B)and/or received (for example, by a WTRU) in the received resource grant.The received resource grant may be a received UL grant.

There may be one or more HARQ processes associated with a given TTI. Forexample, there may be one HARQ process associated with a given TTI whenthe physical layer is not configured for spatial multiplexing (forexample, UL spatial multiplexing). There may be two HARQ processassociated with a given TTI when the physical layer is configured forspatial multiplexing (for example, UL spatial multiplexing). A TB may betransmitted on a PUSCH.

A WTRU may be configured to use a number of HARQ processes in the ULand/or DL such as 8 HARQ processes in the UL and in the DL. The numberof HARQ processes may be used to determine the amount of memory (forexample, the amount of soft buffer memory) the WTRU may need to maintainto support transmissions and retransmissions. Based on the maximum TBsize and the number of HARQ processes, the WTRU may determine themaximum amount of memory it may need to maintain to supporttransmissions and retransmissions in the UL and/or the DL. The maximumTB size may be a function of the TTI length, the allowed MCSs, and/orother parameters.

For example, a system (for example, an LTE-A system) may use a TTIlength (for example, a first TTI length) that may be fixed or known (forexample, 1 ms). A WTRU may have a memory size that may be associatedwith a number of HARQ processes (for example, 8 HARQ processes) in theUL and/or DL. The memory size for each HARQ process may correspond tothe maximum TB size for the TTI length that may be fixed or known.

Another TTI (for example, a second TTI) such as an sTTI may be used byor for a WTRU, for example, to reduce latency in the system. The secondTTI may be shorter than the first TTI and may be referred to as a shortTTI (sTTI). The first TTI may be used at least sometimes (for example,some or all of the time). The second TTI may also be used at leastsometimes (for example, some or all of the time). The first and secondTTIs may sometimes (for example, some or all of the time) be usedconcurrently or in adjacent time intervals. For example, the first TTImay be used in a first subframe and the second TTI may be used in thenext adjacent subframe.

Examples for handling the HARQ processes and HARQ buffers for multipleTTI lengths are provided herein. In an example, separate HARQ processesand HARQ buffers may be used for each of the first and second TTIlengths.

FIG. 11 is a diagram illustrating an example of separate HARQ processesand HARQ buffers for two TTI lengths. For example, the two TTI lengthsmay be TTI 1 and TTI 2. As shown in the example in 1100, separate HARQprocesses and HARQ buffers may be used for each of TTI 1 and TTI 2. Forexample, HARQ process buffers 1110 may be used for TTI 1 and HARQprocess buffers 1160 may be used for TTI 2. However, without reducingthe number of HARQ processes, separate processes and buffers may resultin an increase in the memory that may be needed in the WTRU. For theexample in FIG. 11, memory may be needed for the 8 HARQ processes 1110for TTI 1 plus the 8 HARQ processes 1160 for TTI 2. This arrangement maybe wasteful of memory, for example, when one of the TTIs (for example,TTI 1 or TTI 2) may be used more frequently than the other TTI (forexample, TTI 2 or TTI 1) during a period of time. In the example, 8 HARQprocesses are used for TTI 1 and 8 HARQ processes are used for TTI 2.Any number of HARQ processes may be used for each of TTI 1 and TTI 2 andstill be consistent with the examples described herein.

In an example, a number of processes may be reduced, for example, tomaintain memory size. For example, a number of HARQ processes may bereduced to maintain memory size.

FIG. 12 is a diagram illustrating another example of separate HARQprocesses and HARQ buffers for two TTI lengths. As shown in an examplein diagram 1200, HARQ process buffers 1210 may be used for TTI 1, forexample when TTI 1 may be used without TTI 2. HARQ process buffers 1260may be used when TTI 1 and TTI 2 may both be used. TTI 1 may be a normalTTI. TTI 2 may be an sTTI.

In the example shown in FIG. 12, a second TTI (for example, TTI 2) maybe an sTTI and may be half the length of the first TTI (for example, TTI1). For HARQ process buffers 1260, the number of processes for the firstTTI may be reduced to 6 and the number of processes for the second TTImay be configured to be 4 so that an equivalent amount of memory may beused as for the memory needed for 8 processes for the first, longer TTIfor HARQ process buffers 1210. Reducing the number of processes, forexample of the first or second TTI from 8 as in 1210 and 1110 for TTI 1and 1160 for TTI 2, may, however, delay new transmissions due toretransmission since fewer buffers may be available for new data whileold data is being retransmitted. Also, fixing or semi-staticallyconfiguring the number of HARQ processes or buffers per TTI length mayresult in inefficiencies, for example, since sometimes one TTI may beused more than another.

Thus, further alternate means for sharing the memory for HARQ processingamong the multiple TTIs are disclosed in examples provided herein.Specifically, in one or more examples, one or more of the memory,buffers, or processes for HARQ processing may be shared or partitionedamong two or more TTI lengths. The sharing or partitioning may beconfigured and/or indicated, for example, dynamically. It will beappreciated that TTI and TTI length may be used interchangeably herein.

A first TTI may be or may correspond to one or more of the following: aregular TTI, a normal TTI, a nominal TTI, a long TTI, a longest TTI thata WTRU may use or be configured to use, a subframe (SF), 1 ms, a set ofsymbols (for example, 14 symbols), among others. The first TTI may bereferred herein to as an nTTI. The nTTI may be referred to as a normalTTI.

A second TTI may be or may correspond to one or more of the following: ashort TTI, a reduced length TTI, a TTI shorter than nTTI, part of asubframe, less than a subframe, less than 1 ms, a timeslot, a set ofsymbols (for example, a number of symbols such as 1, 2, 3, 4, and 7),among others. The second TTI may be referred to herein as an sTTI.

A HARQ process or buffer that may be used for an nTTI may be used formultiple sTTIs. The number of sTTIs for which a HARQ process or buffermay be used may be a function of the sTTI length and/or the nTTI length.For example, the number of sTTIs for which a HARQ process or buffer maybe used may be a function of TTI length, for example sTTI length, whichmay be configured. A WTRU may determine the number of sTTIs for which aHARQ process or buffer may be used, for example, based on at least ansTTI length, for example the longest sTTI length that may be configured.An eNode-B may configure a WTRU to use one or more sTTIs of one or morelengths and the WTRU may determine the number of sTTIs for which a HARQprocess or buffer may be used based on at least an sTTI length that theWTRU may be configured to use.

The number of sTTIs for which a HARQ process or buffer may be used maybe configured by the eNode-B, for example, via higher layer signalingsuch as RRC signaling. A WTRU may receive the configuration. A WTRU maydetermine the number of sTTIs for which a HARQ process or buffer may beused based on at least the configuration.

For example, sTTI may be half the length of nTTI. One HARQ process orbuffer for one nTTI may be used for two sTTIs, for example, when an sTTImay be half or less than half the length of nTTI. One HARQ process orbuffer for one nTTI may be used for four sTTIs, for example, when ansTTI may be less than or equal to one fourth the length of nTTI, such aswhen an sTTI may be 3 symbols and an nTTI may be 14 symbols in length.

FIG. 13 is a diagram illustrating an example of linking or sharing HARQprocesses, HARQ buffers or both between two TTI lengths. The two TTIlengths may be nTTI and sTTI in examples described herein. In one ormore embodiments and examples described herein, a HARQ process and aHARQ buffer may be substituted for each other and still be consistentwith the examples provided herein. Furthermore, the phrases HARQ bufferand HARQ process buffer may be used interchangeably herein. The termprocess/buffer may be used to represent a process, a buffer or bothherein. A process/buffer may be a HARQ process/buffer.

In the example shown in diagram 1300, one nTTI HARQ buffer may bepartitioned and/or used for two sTTI HARQ buffers. There may be one ormore nTTI HARQ buffers 1310. In the example 1300, one or more nTTI HARQbuffers 1310 may be partitioned and/or used for one or more sTTI HARQbuffers 1360. For example, nTTI HARQ buffer 2 1320 may be partitionedand/or used for sTTI HARQ buffers 2a 1330 and 2b 1340. Further, nTTIHARQ buffer 4 1350 may be partitioned and/or used for sTTI HARQ buffers4a 1380 and 4b 1370.

An nTTI HARQ buffer may be used for nTTI data or sTTI data. An nTTI HARQbuffer may not be used simultaneously for nTTI data and sTTI data, in anexample. In the example shown in FIG. 13, nTTI HARQ buffers 2 and 4 maybe used for sTTI data and the other nTTI HARQ buffers may be used fornTTI data. A HARQ buffer may represent memory that may be used for aHARQ process. A HARQ buffer may or may not be in a fixed location inmemory. A HARQ buffer may comprise consecutive memory locations,non-consecutive memory locations or both.

FIG. 14 is a diagram illustrating an example timeline for multiple TTIlength usage. In the example shown in diagram 1400, the time periodduring which a transmission occurs is a subframe which may correspond to1 ms. A subframe is a non-limiting example of the time period of atransmission. An nTTI may be the same duration as the time period (forexample, a subframe). An sTTI may be shorter than the nTTI. For example,the sTTI may be half the length of the nTTI or less than half the lengthof the nTTI. In the example 1400, an sTTI may be used in subframes 2, 4and 8, while an nTTI may be used in each of the other subframes. Insubframes 2 and 8, one sTTI may be used. In subframe 4, 2 sTTIs may beused.

For the examples shown in FIGS. 13 and 14, the WTRU may use the HARQprocesses, buffers or both for the data (for example, for transmissionor reception of the data) for the subframes as follows: nTTI in subframe#0 (SF0) may use process/buffer 0, nTTI in SF1 may use process/buffer 1,sTTI in SF2 may use the first half of process/buffer 2 (for example, aprocess/buffer 2a), nTTI in SF3 may use process/buffer 3, a first sTTIin SF4 may use the second half of process/buffer 2 (for example, aprocess/buffer 2b), the second sTTI in SF4 may use the first half ofprocess/buffer 4 (for example, a process/buffer 4a), nTTI in SF5 may useprocess/buffer 5, nTTI in SF6 may use process/buffer 6, nTTI in SF7 mayuse process/buffer 7, and sTTI in SF8 may use the second half ofprocess/buffer 4 (for example, process/buffer 4b). Thus, sTTI data maybe transmitted/received using a next available sTTI buffer amongmultiple HARQ buffers. In this manner, the buffers may be used as neededfor nTTI, sTTI or both. For N HARQ buffers, for example N=8,transmissions/retransmissions in later subframes may reuse the N HARQbuffers.

Examples of the linkage of sTTI and nTTI HARQ processes/buffers areprovided herein. For example, one or more HARQ processes and/or buffersmay be at least one of linked, shared, or overlapped. For example, afirst HARQ process and/or buffer may be linked, shared, or overlappedwith a second HARQ process and/or buffer. In the embodiments andexamples described herein, the terms linked, overlapped, and shared maybe substituted for each other and still be consistent with the examplesprovided herein.

FIG. 13 shows an example in which nTTI HARQ process/buffer k may belinked, shared or overlapped with sTTI HARQ process/buffer ka and sTTIHARQ process/buffer kb, where k=0, 1, . . . 7. For example, nTTI HARQprocess/buffer 0 may be linked, shared or overlapped with sTTI HARQprocess/buffer 0a and sTTI HARQ process/buffer 0b. Further, nTTI HARQprocess/buffer 2 may be linked, shared or overlapped with sTTI HARQprocess/buffer 2a and sTTI HARQ process/buffer 2b. Also, nTTI HARQprocess/buffer 4 may be linked, shared or overlapped with sTTI HARQprocess/buffer 4a and sTTI HARQ process/buffer 4b. This linking, sharingor overlapping may apply to a subset or all of the nTTI and sTTI HARQprocesses/buffers.

FIG. 15 is a diagram illustrating another example of HARQ processes,buffers or both that may be linked, shared or overlapped. As shown indiagram 1500, a first set (for example, a base set) of HARQprocesses/buffers may be linked, overlapped, or shared with a second setof HARQ processes/buffers. In an example, the first set may be all orsome of HARQ processes/buffers 1510 and the second set may be all orsome of HARQ processes/buffers 1560. For example, nTTI HARQ processand/or buffer 2 may be linked, shared, or overlapped with sTTI HARQprocesses and/or buffers 4 and 5. Similarly, nTTI HARQ process and/orbuffer 4 may be linked, shared, or overlapped with sTTI HARQ processesand/or buffers 8 and 9.

FIG. 16 is a diagram illustrating another example of linking, sharing oroverlapping HARQ processes, buffers or both. FIG. 17 is a diagramillustrating a further example of linking, sharing or overlapping HARQprocesses, buffers or both. In particular, FIGS. 16 and 17 show moreexamples of HARQ processes, buffers or both that may be linked, shared,or overlapped. Some processes may be linked to other processes. Someprocesses may not be linked to other processes. Some processes may belinked to other processes that may be linked to additional otherprocesses. In an example, the processes numbered 0-7 in diagram 1600 maybe nTTI processes and the other processes (for example, processes 8-15)may be sTTI processes. In an example, HARQ processes 1610 may be nTTIprocesses and HARQ processes 1660 may be sTTI processes. In diagram1700, the processes numbered 0-5 in may be nTTI processes and the otherprocesses (for example, processes 0a-0d, 1a-1b, 1aa-1bb, and 8-11) maybe sTTI processes. Respective buffers may be used and divided/subdividedfor use according to the assigned processes corresponding thereto (forexample, whether a process is an nTTI process, sTTI process, or sTTIsubprocess).

A WTRU may receive a configuration (for example, a configurationmessage, signal or information) from a base station (for example, aneNode-B), that may indicate that at least one HARQ process/buffer may belinked, shared, or overlapped with another HARQ process/buffer. Theconfiguration may indicate that a first HARQ process/buffer may belinked, shared, or overlapped with a second HARQ process/buffer or oneor more other HARQ process(es)/buffer(s). For example, the configurationmay indicate that HARQ process i may be linked to HARQ processes j andk, where i, j, and k may be integers.

The first HARQ process/buffer may be an nTTI HARQ process/buffer and thesecond or the one or more other HARQ process(es)/buffer(s) may be sTTIHARQ process(es)/buffer(s). The second or other HARQ processes/buffersmay be the same, different, independent, dependent, and/or related fromor to each other.

When a first HARQ process is linked to a second HARQ process, the bufferthat may be used for a TB for the first HARQ process may be used for aTB for the second HARQ process. In an example, the buffer may be a softbuffer. For example, if HARQ process A is linked to HARQ processes B andC, use of HARQ process B and/or C, for example indication to use HARQprocess B and/or C, may indicate that data associated with HARQ processA may be overwritten or discarded. Data associated with HARQ process Band/or C may use at least part of the buffer previously used for HARQprocess A. A subsequent use of HARQ process A may be considered new dataor an indication of new data for HARQ process A. Use of HARQ process A,for example an indication to use HARQ process A, may indicate that dataassociated with HARQ process B and/or C may be overwritten or discarded.Data associated with the subsequent HARQ process A may use the buffer orbuffers previously used for HARQ process B and/or C. A subsequent use ofHARQ process B and/or C may further be considered new data or anindication of new data for the respective HARQ process or processes.

Examples of a determination of a HARQ process/buffer to use are providedherein. For example, an eNode-B may manage, configure, and/or indicateat least one HARQ process/buffer a WTRU may use for a (for example,each) transmission, for example via signaling transmitted to the WTRU.

A WTRU may receive an indication as to which HARQ process to use for atransmission or reception of data. The indication may be received, forexample, dynamically, in a control channel (for example, a DL controlchannel) such as a PDCCH, an EPDCCH, an S-PDCCH (which may be referredto as an sPDCCH), an M-PDCCH (which may be referred to as an mPDCCH), aNB-PDCCH, and the like. The indication may be received in controlinformation (for example, a DL control information (DCI)) that may becarried by a control channel. The control channel, control informationor both may provide a grant (for example that may indicate resources)for data to transmit or receive, and the grant may include an indicationas to which HARQ process to use for a transmission or reception of data.The indication as to which HARQ process to use may be or may include aHARQ process ID or number.

A transmission may be in the UL or the SL. Reception may be in the DL orthe SL. Data may be used to represent at least one of a TB, multipleTBs, a DL channel, or a UL channel. A DL channel may, for example, be aPDSCH or a short PDSCH (sPDSCH). A UL channel may be a PUSCH or a shortPUSCH (sPUSCH). Reception of/on a channel may include combiningrepetitions of/on a channel, for example, when operating with coverageenhancements. Transmission of/on a channel may include transmittingrepetitions of/on a channel, for example, when operating with coverageenhancements.

In an example, a WTRU may receive an indication (for example, via amessage, a signal, a control channel or control information such as in aDCI format) to use a HARQ process or HARQ buffer that may be at leastone of linked, shared, or overlapped with another HARQ process orbuffer. The indication may be received in a control channel and/orcontrol information (for example, a DCI) that may include a grant forresources such as UL or DL resources. An eNode-B may provide theindication. A WTRU may receive the indication, for example from theeNode-B. The WTRU may use the indication for processing andconfiguration.

An eNode-B may provide and/or a WTRU may receive at least one of thefollowing indications (for example, in a DL control channel or in a DCIthat may include a grant such as a DL or UL grant): an indication of aprocess/buffer to use; an indication of the process/buffer to use fordata (for example, DL data or UL data) associated with a grant (forexample, a DL grant or UL grant)); an indication of a process/buffer touse for a data associated with a grant that may be linked, shared, oroverlapped with another process/buffer; an indication of a baseprocess/buffer (for example, an nTTI process/buffer); an indication of aprocess/buffer (for example, a sTTI process/buffer) that may be linked,shared or overlapped with a base process/buffer; an indication of asub-buffer or sub-process to use, for example, for sTTI transmissionand/or reception; an indication of a TTI length for the data; anindication that a TTI for the data may be an sTTI or an nTTI; and anindication of whether the data for the process/buffer is new data orretransmitted data (for example, a new data indicator (NDI) may betoggled to indicate new data. The NDI may be provided in the grant. TheNDI may be provided in or with the indication as to which HARQ processto use.

A WTRU may determine that one or more HARQ processes and/or buffers maybe linked, shared, or overlapped with one or more other HARQ processesand/or buffers, for example, based on at least signaling and/orconfiguration that may be semi-static and/or dynamic. The signalingand/or configuration may be received from an eNode-B.

Hereinafter, a HARQ process which may be associated with a first TTIlength may be referred to as an nHARQ, and a HARQ process which may beassociated with a second TTI length may be referred to as an sHARQ. Thefirst TTI length may be longer than the second TTI length. A soft buffersize for nHARQ may be larger than that for sHARQ. One or more sHARQs maybe linked, shared, or overlapped with an nHARQ. One or more sets ofsHARQs may be linked with an nHARQ (for example, a single nHARQ). A setof sHARQs that may be linked with an nHARQ may be dynamically indicatedfrom/by a DCI. One or more sets of sHARQs may be predefined, configured,or determined based on a TTI length, for example the TTI lengthassociated with the sHARQ. One or more sets of sHARQs may be determinedbased on a WTRU capability.

A WTRU may receive a DCI associated with a DL, UL, or SL transmissionand the DCI may include a HARQ process ID or number and HARQ linkageinformation. For example, a WTRU may receive a DCI for a UL transmissionwith a first TTI length and the DCI may indicate an nHARQ ID or number(for example, a HARQ process ID or number for a first TTI length) andone or more sHARQ IDs or numbers which may be linked. It will beappreciated that the terms process ID or process number may be usedinterchangeably herein.

The first type HARQ process number (for example, nHARQ number) may beused for a data transmission and retransmission (for example, saved orto be saved in a soft buffer).

The second type HARQ process number(s) (for example, sHARQ numbers) maybe used to flush the buffer. For example, the soft buffer(s) associatedwith the second type HARQ process numbers may be flushed and used forthe first type HARQ process number (for example, nHARQ number). Thesecond type HARQ process numbers may be indicated in a bit field in theDCI. The number of second type HARQ processes may be determined (forexample, by the eNode-B and/or WTRU) based on the first TTI lengthand/or the second TTI length. For example, if the first TTI length isdouble that of the second TTI length, two second type HARQ processes maybe indicated from the DCI.

The presence of the second type HARQ process numbers (for example, sHARQnumbers) may be determined based on one or more of following: a DCItype, an RNTI type, a higher layer configuration, a TTI lengthassociated with a HARQ process, and a transmission scheme associatedwith the HARQ process.

A DCI type may be used. For example, a first DCI type may include thefirst type HARQ process number only and a second DCI type may includethe first type HARQ process number and the second type HARQ processnumber(s). A WTRU may monitor for the first DCI type and the second DCItype in a WTRU-specific search space.

An RNTI type may be used. For example, a DCI with a first RNTI type (forexample, a cell RNTI (C-RNTI)) may include the first type HARQ processnumber only. A DCI with a second RNTI type (for example, HARQ-C-RNTI(H-C-RNTI)) may include the first and second type HARQ processnumber(s).

A WTRU may monitor for, receive, decode, and/or attempt to decode afirst DCI type in a first subset of subframes and monitor for, receive,decode, and/or attempt to decode a second DCI type in a second subset ofsubframes. The first subset of subframes and the second subset ofsubframes may be non-overlapped. Alternatively, the first subset ofsubframes and the second set of subframes may be partially or fullyoverlapped.

The subset of subframes for the first DCI type and/or the second DCItype may be determined based on a subframe number and/or system framenumber (SFN).

The first DCI type may be monitored/received in a first subset of PDCCHcandidates and the second DCI type may be monitored/received in a secondsubset of PDCCH candidates. The first subset of PDCCH candidates and thesecond subset of PDCCH candidates may be non-overlapped.

FIG. 18 is a diagram illustrating an example of linking or sharing HARQprocesses, buffers or both with a dynamic indication. In an exampleshown in diagram 1800, a WTRU may receive a first type DCI which doesnot indicate any second HARQ process numbers when nHARQ 0 may beindicated and the WTRU may receive a second type DCI which may indicatesecond HARQ process numbers (for example, sHARQ 0 and sHARQ 2) whennHARQ1 may be indicated, and so forth. As shown in FIG. 18, nHARQ1,nHARQ3, nHARQ4 and nHARQ6 are each linked to two sHARQs that may beindicated in the second type DCI. The second type DCI may be received inan sTTI or nTTI.

The linkage, sharing, and/or overlapping of HARQ processes and/orbuffers may be a function of the sTTI length or lengths that may beused. The WTRU may determine the linkage, sharing, and/or overlapping ofHARQ processes and/or buffers based on the sTTI length or lengths thatmay be used, for example, based on the longest sTTI length that may beused. The sTTI length or lengths that may be used may be configured, forexample, by an eNode-B. The sTTI length or lengths that may be used maybe WTRU-specific.

Examples of DL operation with HARQ processes are provided herein. A DLprocedure (for example, MAC procedure) that may be related to HARQprocesses and/or HARQ buffers may be used and/or modified according toone or more embodiments described herein.

An example procedure, which may be referred to as example Procedure 1,for DL data reception at the WTRU may include one or more of thefollowing operations. It will be appreciated that one or more of thefollowing operations may be performed serially, concurrently, or in anoverlapping manner, and, unless explicitly stated, no inference shouldbe drawn regarding the order of performance of the operations, portionsthereof, or the performance of the operations exclusively without theoccurrence of intervening or intermediate operations.

Example Procedure 1 may include one or more of the following operations.The WTRU may receive a DCI indicating a DL grant with HARQ process Aidentified. There may be one TB (for example, there may be no use ofspatial diversity). The WTRU may determine whether the data is a newtransmission or a retransmission. For example, the WTRU may determine ifan NDI has been toggled compared to a value of the previous receivedtransmission corresponding to the TB. The WTRU may determine that thedata is a new transmission, for example, if the WTRU determines that NDIhas been toggled. The WTRU may attempt to decode the received data, forexample, if the WTRU determines the data is a new transmission. The WTRUmay replace the data in the soft buffer for the TB with the data theWTRU attempted to decode, for example, if the WTRU did not successfullydecode the data. The WTRU may combine the received data with the datacurrently in the buffer for the TB and attempt to decode the combineddata, for example, if the WTRU determines the data is a retransmission.The WTRU may send an ACK or NACK, for example, based on whether or notit successfully decoded the data. The WTRU may send the ACK or NACK tothe eNode-B

At the end of example Procedure 1, there may be data in the soft bufferfor the HARQ Process A TB. The WTRU may keep the data in the bufferuntil the WTRU receives an indication to use the buffer for new data,for example, as described for example Procedure 1. Alternatively, theWTRU may reuse the memory associated with the buffer, for example, forthe same or another HARQ process, once it has determined that itsuccessfully decoded the data for HARQ Process A.

Example Procedure 1 may be modified for the use of linked HARQprocesses. The linked HARQ processes may be those described herein.

Further, a determination of whether data for a TB associated with a HARQprocess may be new data may be based on at least whether a transmissionwas received for a linked HARQ process since receiving a previoustransmission corresponding to the TB. It will be appreciated that one ormore of the following operations may be performed serially,concurrently, or in an overlapping manner, and, unless explicitlystated, no inference should be drawn regarding the order of performanceof the operations, portions thereof, or the performance of theoperations exclusively without the occurrence of intervening orintermediate operations.

For example, a WTRU may perform one or more of the following operations.A WTRU may receive a DCI indicating a DL grant for HARQ process A forwhich there may be one TB.

The WTRU may determine that a HARQ process linked to HARQ process A,such as HARQ process B or C, received a transmission since the previousreceived transmission corresponding to this TB.

The WTRU may consider or determine the NDI to have been toggled and/ormay consider or determine this transmission to be a new transmission.The WTRU may make this determination based at least on its determinationthat a HARQ process linked to HARQ process A received a transmissionsince the previous received transmission corresponding to this TB. TheWTRU may make this determination independent of whether the NDI wasactually toggled since the previous received transmission correspondingto this TB.

The WTRU may release at least some or all of the buffer memoryassociated with a HARQ process when a linked HARQ process receives newdata. Release of the memory may be for another use such as use foranother HARQ process that may be a linked HARQ process. For example, theWTRU may release at least some or all of the buffer memory associatedwith HARQ Process A when the WTRU receives new data for a HARQ processlinked to HARQ Process A, such as HARQ process B or C. Additionally oralternatively, the WTRU may release at least some or all of the buffermemory associated with HARQ Process B and/or C, for example, when theWTRU receives new data for a HARQ process linked to HARQ Process Band/or C, such as HARQ process A. Accordingly, a WTRU may use at leastsome of the same buffer memory for linked HARQ processes.

In the examples and embodiments described herein, one TB may be used fornon-limiting exemplary purposes. The embodiments and examples may beextended to multiple TBs and still be consistent with the examplesprovided herein.

Examples of UL operation with HARQ processes are provided herein. A ULprocedure (for example, a MAC procedure) that may be related to HARQprocesses and/or HARQ buffers may be used, modified or both.

An example procedure, which may be referred to as example Procedure 2,for UL data transmission by the WTRU may include one or more of thefollowing operations. It will be appreciated that one or more of thefollowing operations may be performed serially, concurrently, or in anoverlapping manner, and, unless explicitly stated, no inference shouldbe drawn regarding the order of performance of the operations, portionsthereof, or the performance of the operations exclusively without theoccurrence of intervening or intermediate operations. For example, aWTRU may perform one or more of the following operations.

The WTRU may receive a DCI indicating a UL grant with HARQ process Aidentified. The HARQ process may be identified, for example, whenasynchronous HARQ may be used. The HARQ process may be identified, forexample, when synchronous HARQ may be used, for example, when the WTRUmay use or be configured to use sTTI at least sometimes. The HARQprocess may be identified when the WTRU may be configured to use sTTI atleast sometimes. For example, the HARQ process may be identified for ansTTI transmission. The HARQ process may be identified for an nTTItransmission when the WTRU may be configured to use sTTI at leastsometimes.

The WTRU may determine whether the data, for example, data that may betransmitted by or for the identified HARQ process, is a new transmissionor a retransmission. For example, the WTRU may determine if an NDI (forexample, in the associated HARQ information) has been toggled comparedto a value in or for the previous transmission of this HARQ process. TheWTRU may determine that the data is a new transmission, for example, ifthe WTRU determines that NDI has been toggled. Additionally oralternatively, the WTRU may determine that the data is a newtransmission if the HARQ buffer of the identified HARQ process is empty.

The WTRU may do one or more of the following, for example if the WTRUdetermines that the data is for a new transmission. The WTRU may obtaina TB (for example, a MAC protocol data unit (PDU)), which may be, forexample a new TB. Further, the WTRU may deliver the TB to the identifiedHARQ process. Also, the WTRU may instruct the identified HARQ process totrigger a new transmission.

The WTRU may do one or more of the following, for example, if the WTRUdetermines that the data is not for a new transmission. The WTRU maydeliver the UL grant and/or the HARQ information (for example,redundancy version) to the identified HARQ process. Further, the WTRUmay instruct the identified HARQ process to generate a retransmission.The retransmission may be, for example, an adaptive or non-adaptiveretransmission.

The WTRU or HARQ process may transmit or retransmit the TB of the HARQprocess. The TB of the HARQ process may be, for example, the TB in theHARQ buffer of the identified HARQ process.

The WTRU may flush the HARQ buffer of the identified HARQ process whenthe number of retransmissions reaches or exceeds a threshold value thatmay be configured. In an example, in this way, the WTRU may empty theHARQ buffer of the identified HARQ process when the number ofretransmissions reaches or exceeds a threshold value that may beconfigured.

The procedures described herein may be modified for the use of linkedHARQ processes. For example, a determination of whether data that may betransmitted by or for a first HARQ process may be new data may be basedon at least whether a transmission (for example, a new datatransmission) was requested or made for a second HARQ process (forexample, a linked HARQ process) since the previous transmission of thefirst HARQ process.

A WTRU may flush at least part or all of the HARQ buffer of a first HARQprocess when a transmission (for example, a new data transmission) isrequested or made for a second HARQ process (for example, a linked HARQprocess). For example, for a first HARQ process (for example, HARQprocess A) linked to two HARQ processes (for example, HARQ processes Band C), the WTRU may flush the HARQ Process B buffer and the HARQProcess C buffer when a data transmission (for example, a new datatransmission) is requested for HARQ Process A. The WTRU may flush atleast part or all of the HARQ Process buffer A when a data transmission(for example, a new data transmission) may be requested for HARQ ProcessB or HARQ Process C.

Referring to FIG. 17, the WTRU may flush the HARQ buffer of HARQ process0, for example, when a data transmission (for example, a new datatransmission) is requested for at least one of HARQ processes 0a, 0b,0c, or 0d. The WTRU may flush at least one or all of the HARQ buffersfor HARQ processes 0a, 0b, 0c, and 0d, when a data transmission (forexample, a new data transmission) is requested for HARQ process 0. Atransmission request may be made via a DCI and/or an UL grant. The DCImay include the UL grant.

In another example, the WTRU may perform or be configured to perform oneor more of the following. The WTRU may receive a DCI indicating an ULgrant with HARQ process A identified. The WTRU may determine whether thedata, for example, that may be transmitted by or for the identified HARQprocess, is a new transmission or a retransmission. The WTRU maydetermine that the data is a new transmission, for example, if a datatransmission (for example, a new data transmission) was requested for alinked HARQ buffer or linked HARQ process since the last transmission ofthe identified HARQ process. The WTRU may determine that the data is anew transmission, for example, if the WTRU determines that an NDI hasbeen toggled. The WTRU may determine that the NDI has been toggled, forexample, if a data transmission (for example, a new data transmission)was requested for a linked HARQ buffer or linked HARQ process since thelast transmission of the identified HARQ process. The WTRU may transmitor retransmit for the identified HARQ process based on the determinationof new transmission or retransmission.

In the embodiments and examples described herein, the terms flush,empty, release, reuse, and overwrite may be substituted for each otherand still be consistent with the examples provided herein. The termsflush, empty, and/or release of a buffer or memory may be used to meanthat the memory, for example, the memory associated with the buffer, maybe used, reused, and/or overwritten.

The buffer or memory may be associated with a first process and may beused or reused by a second process. Overwriting may be by data (forexample, bits) for or associated with a second process, for example,data for a buffer associated with a second process. The second processmay be the same as the first process, for example, with new dataindicated. The second process may be a process other than the firstprocess, for example, with new data indicated. The second process may bea process linked to the first process. A process may be a HARQ process.A buffer may be a HARQ buffer. A memory may be soft buffer memory. Amemory may be memory for DL-SCH data, PDSCH, UL shared channel (UL-SCH)data, and/or PUSCH. A buffer associated with the second process may belinked, shared, and/or overlapped with a buffer associated with thefirst process.

A WTRU may assume or may be configured to assume that it does not needto reserve or maintain memory for data associated with a second HARQprocess, for example, when the WTRU may be using or may be indicated touse a first HARQ process that may be linked to the second HARQ process.In an example, the memory may be separate or additional memory.

A WTRU may be configured to assume that it does not need to reserve ormaintain memory (for example separate or additional memory) for dataassociated with a second HARQ process when the WTRU may be using or maybe indicated to use a first HARQ process that may be linked to thesecond HARQ process, for example, until the WTRU receives an indication(for example, an explicit indication) for data transmission or reception(for example, new data transmission or reception) for the second HARQprocess. The indication may be from an eNode-B.

FIG. 19 is a diagram illustrating an example of HARQ buffer sharing bydifferent HARQ processes. In an example, a WTRU may allocate a TB to aHARQ process for UL transmission. In an example shown in diagram 1900, aWTRU may link a first HARQ process and a second HARQ process, whereinthe first HARQ process is associated with a first HARQ buffer and afirst TTI length and the second HARQ process is associated with thefirst HARQ buffer and a second TTI length 1910. The WTRU may transmit afirst TB using the linked first HARQ process and the first HARQ buffer1920. Also, the WTRU may receive a UL grant 1930. The WTRU may thendetermine that the received UL grant is for a new transmission for thelinked second HARQ process 1940. Further, the WTRU may release the firstHARQ buffer based on a determination that the received UL grant is forthe new transmission for the linked second HARQ process 1950. Inaddition, the WTRU may generate a second TB for the new transmission1960. In another example, the WTRU may allocate a second TB for the newtransmission. In a further example, the WTRU may obtain a second TB forthe new transmission, may assemble a second TB for the new transmissionor both. In an additional example, the WTRU may receive a second TB forthe new transmission.

Moreover, the WTRU may store the second TB in the first HARQ buffer1970. Further, the WTRU may transmit the second TB using the linkedsecond HARQ process and the first HARQ buffer 1980.

The second TB may overwrite or replace some or all of the first TB inthe first HARQ buffer. The first HARQ buffer may, for example be usedfor the second TB when the first TB is no longer needed. The first TBmay no longer be needed when it is successfully received, for example byan eNode-B for UL transmission or by the WTRU for DL reception. In anexample, the first TTI length may be an nTTI length and the second TTIlength may be an sTTI length or vice versa.

In an example, the first TB and the second TB may be MAC PDUs. Further,the first TB may contain data associated with a first TTI and the secondTB may contain data associated with a second TTI.

DL transmissions may use another example of HARQ buffer sharing bydifferent HARQ processes. For example, a WTRU may allocate a TB to aHARQ process for DL reception. In an example, a WTRU may link a firstHARQ process and a second HARQ process, wherein the first HARQ processis associated with a first HARQ buffer and a first TTI length and thesecond HARQ process is associated with the first HARQ buffer and asecond TTI length. Further, the WTRU may receive data for a first TBusing the linked first HARQ process and the first HARQ buffer. The WTRUmay also receive a DL grant. The WTRU may then determine that thereceived DL grant is for the reception of a new transmission for thelinked second HARQ process. Further, the WTRU may release the first HARQbuffer based on a determination that the received DL grant is for thereception of the new transmission for the linked second HARQ process.Also, the WTRU may receive data for a second TB for the new transmissionusing the linked second HARQ process and the first HARQ buffer. Further,the WTRU may replace the data in the first HARQ buffer with the datareceived for the second TB.

In another example, the HARQ buffers may be used for soft combining. Forexample, the first HARQ buffer may be used for soft combining. In anadditional example, the HARQ buffers may be located in soft buffermemory. For example, the first HARQ buffer may be located in soft buffermemory.

A WTRU may have a set of capabilities that it may signal or send to aneNode-B. The capabilities may include its memory capabilities, forexample, in the DL, UL, and/or SL.

For example, a WTRU may have a capability for the number of soft channelbits it may support in the DL. The number of soft channel bits mayrepresent the number of soft channel bits available for HARQ processes(for example, in the DL). The number of soft channel bits may be thenumber of soft channel bits available for nTTI HARQ processing.

The WTRU may have a capability that may indicate a separate number ofsoft channel bits that the WTRU may have available for sTTI HARQprocessing. Also, the WTRU may have a capability that may indicate thatthe WTRU may not have additional soft channel bits available for sTTIHARQ processing and, for example, the WTRU may use or may need to usethe bits available for nTTI HARQ processing for sTTI HARQ processing aswell.

The WTRU may use linkage, sharing, and/or overlapping of HARQ processesand/or buffers, for example, when the WTRU does not have additional, orenough additional, soft channel bits available for sTTI HARQ processing.An eNode-B may configure a WTRU to use linkage, sharing, and/oroverlapping of HARQ processes and/or buffers, for example, when the WTRUdoes not have additional, or enough additional, soft channel bitsavailable for sTTI HARQ processing. The eNode-B may configure a WTRU touse linkage, sharing, and/or overlapping of HARQ processes and/orbuffers based at least on its capability for bits for sTTI HARQprocessing.

A WTRU may have a capability that may indicate or may be used todetermine the amount of memory that the WTRU may support in the UL. Forexample, the WTRU may have a capability for Maximum UL-SCH transportblock bits transmitted within a TTI that may be used to determine theamount of memory the WTRU may support in the UL.

The WTRU may have a capability that may indicate that the WTRU may nothave additional memory available for sTTI HARQ processing and, forexample, the WTRU may or may need to use the memory available for nTTIHARQ processing for sTTI HARQ processing as well. Also, the WTRU may uselinkage, sharing, and/or overlapping of HARQ processes and/or buffers,for example, when the WTRU does not have additional, or enoughadditional, memory available for sTTI HARQ processing.

An eNode-B may configure a WTRU to use linkage, sharing, and/oroverlapping of HARQ processes and/or buffers, for example, when the WTRUdoes not have additional, or enough additional, memory available forsTTI HARQ processing. The eNode-B may configure a WTRU to use linkage,sharing, and/or overlapping of HARQ processes and/or buffers based atleast on the WTRU's capability for memory for sTTI HARQ processing.Configuration and/or use of linkage, sharing, and/or overlapping of HARQprocesses and/or buffers may be separate and/or different for at leastone of UL, DL, and SL (for example, based on the WTRU's capabilities foreach).

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed:
 1. A method for use in a wireless transmit/receive unit(WTRU), the method comprising: receiving, in a first subframe, downlinkcontrol information (DCI) including information indicating a grant for aphysical downlink shared channel (PDSCH) transmission and informationindicating physical uplink control channel (PUCCH) resources; receiving,in the first subframe, the PDSCH transmission based on the informationindicating the grant; and transmitting, in the first subframe, firstacknowledgement (ACK)/negative ACK (NACK) information in a PUCCHtransmission using the PUCCH resources, wherein the first ACK/NACKinformation is based on the PDSCH transmission.
 2. The method of claim1, wherein the first ACK/NACK information is transmitted in a time slotin the first subframe different from a time slot in the first subframein which the DCI is received.
 3. The method of claim 1, wherein thePUCCH transmission has a duration of one or two symbols.
 4. The methodof claim 1, further comprising: receiving configuration informationregarding a downlink portion of the first subframe and an uplink portionof the first subframe, wherein the PDSCH transmission is received in thedownlink portion of the first subframe, and wherein the first ACK/NACKinformation is transmitted in the uplink portion of the first subframe.5. The method of claim 1, further comprising: receiving WTRU-specificconfiguration information regarding a number of symbols for receivingthe PDSCH transmission; and receiving the PDSCH transmission in thenumber of symbols for receiving the PDSCH transmission.
 6. The method ofclaim 1, wherein the DCI includes a hybrid automatic repeat request(HARQ) process identifier associated with the PDSCH transmission.
 7. Themethod of claim 1, wherein the PDSCH transmission is received over anumber of symbols different from a number of symbols for a reception ofa retransmission of the PDSCH transmission.
 8. The method of claim 1,wherein second ACK/NACK information is transmitted on the PUCCH in atleast one of the first subframe and a second subframe.
 9. A wirelesstransmit/receive unit (WTRU) comprising: a transceiver; and a processoroperatively coupled to the transceiver; wherein: the transceiver isconfigured to receive, in a first subframe, downlink control information(DCI) including information indicating a grant for a physical downlinkshared channel (PDSCH) transmission and information indication physicaluplink control channel (PUCCH) resources; the transceiver is configuredto receive, in the first subframe, the PDSCH transmission based on theinformation indicating the grant; and the processor and the transceiverare configured to transmit, in the first subframe, first acknowledgement(ACK)/negative ACK (NACK) information in a PUCCH transmission using thePUCCH resources, wherein the first ACK/NACK information is based on thePDSCH transmission.
 10. The WTRU of claim 9, wherein the first ACK/NACKinformation is transmitted in a time slot in the first subframedifferent from a time slot in the first subframe in which the DCI isreceived.
 11. The WTRU of claim 9, wherein the PUCCH transmission has aduration of one or two symbols.
 12. The WTRU of claim 9, wherein thetransceiver is further configured to receive information regarding adownlink portion of the first subframe and an uplink portion of thefirst subframe, wherein the PDSCH transmission is received in thedownlink portion of the first subframe, and wherein the first ACK/NACKinformation is transmitted in the uplink portion of the first subframe.13. The WTRU of claim 9, wherein the transceiver is further configuredto receive WTRU-specific information regarding a number of symbols forreceiving the PDSCH transmission; and wherein the transceiver is furtherconfigured to receive the PDSCH transmission in the number of symbolsfor receiving the PDSCH transmission.
 14. The WTRU of claim 9, whereinthe DCI includes a hybrid automatic repeat request (HARQ) processidentifier associated with the PDSCH transmission.
 15. The WTRU of claim9, wherein the PDSCH transmission is received over a number of symbolsdifferent from a number of symbols for a reception of a retransmissionof the PDSCH transmission.
 16. The WTRU of claim 9, wherein secondACK/NACK information is transmitted on the PUCCH in at least one of thefirst subframe and a second subframe.
 17. The method of claim 1, whereinthe DCI is received with a cell radio network temporary identifier(C-RNTI).
 18. The WTRU of claim 9, wherein the DCI is received with acell radio network temporary identifier (C-RNTI).